I haven't gotten that question yet, but very good pickup!
The short and simple answer is - PRICE.
This was a "new car" purchase for my family and an upgrade for me from my Honda Pilot. I grew up in CO and have always wanted a great overlanding rig. A new vehicle purchase was spurred by the arrival of our second child. One more mouth to feed, diapers, daycare...$$$$ Anyway, the Tahoe is where the entire family landed on agreement.
So, it took me all of a week to realize my great new big 4WD rig was actually the unofficial soccer mom transport of the country. Then we took our first camping trip up north in the Maine woods and I just about ripped off the front lower plastic air deflector. I was basically plowing rocks on the trail. The decision was made, mostly by me, to modify the Tahoe so that I was more capable off road. I used the z71 Midnight Edition as my model to work from.
I did a fair amount of research, much on this forum, regarding suspension upgrades, lift/level kits, etc. I also researched tires - I wanted something bigger and similar to a MT, but somewhat practical since I'm only off road about 5-10% of my total miles driven (bummer!). If you look back, particularly at previous model years (pre-2015 Tahoe) you'll see that Billstein is a primary solution/product in peoples mod projects. Time and time again this shock setup kept coming up. I have a +1" rear coil spacer running on the Tahoe so I needed to provide a shock that would work on my truck AND work for +1" lift. The Billstein B8 5100 seemed like a great solution at a fair price. Proven record. Plus a major upgrade from the OEM rear shock absorber air compressed setup on LTZ trims. FYI - I purchased a new pair of z71 rear coils springs and installed them when the rear coil spacer and rear Billstein shocks went in. To my surprise, Chevy has 5 different rear coil springs they use under different trim/options on the Tahoes.
Up front was another beast entirely. I wanted to increase my off road capabilities so that meant improving the approach angle and total ground clearance. Yes - I get to lift the truck! No - wife says too expensive and too big, "we can barely get in now" she said. I was able to sell her on the modification to the front bumper. She wasn't thrilled, but she did like the idea of me adding tow hooks and the skid plates. Approach angle issue solved.
Now for height. I started looking at leveling the truck, but quickly decided that is not the OPTIMAL way to increase ride height. Rather inexpensive up front, but I figured I would be unhappy with the overall ride quality. Also, the leveling kit is used with your EXISTING shocks. The LTZ trim comes standard with Chevy's Magneride suspension system. Not sure how familiar you are with this, but basically all four corners' shocks are "plugged" into the computer, literally, and buffeting is supposed to occur instantaneously between computer and shock. Something along those lines. But my front right magneride shock was replaced under the Certified Pre Owned policy for free when I made the vehicle purchase. 36k miles. How long until original front left shock needed to be replaced? Not under warranty. Chevy charges anywhere between $1200 - $2500 for new magneride shock(s) up front. So my budget was set, stay under $1200 on all front suspension work.
Enter problem #2 of the LTZ magneride - it's hooked to the computer! You can't just install any old front shock that fits because then you're throwing service messages on your dash every minute. Also, the magneride shock is designed slightly differently than many similar coilover setups in that the mounting bracket is smaller than standard. In other words, the shock absorbers that fit the LS and LT trims DO NOT fit on an LTZ. That's when I discovered Xineeering out of FL. Max, owner, is great, really smart computer guy/former car industry software. Now he likes to modify corvettes and help people speed around. But, his electronics apply to the LTZ magneride shocks because that's what the Corvette's platform uses. Xineering sent me 8 plastic electronic pieces that plugged right into the shock absorber/computer line at each corner at the top of the original shock absorber. These pieces tell the computer everything is fine with the magneride. Now, I could install any shock absorber I wanted that could fit up front. That meant an entirely new front coilover, not just a shock absorber.
Product choices were fairly limited and quite expensive. Ie: Fox 2.5 with Reservoirs or Kings... that purchase alone would have broke my budget.
I settled on the Fox 2.0 because they offered the adjustable ride height, solved the problem of needing to install an entire coilover with shock, and the 2.0 pretty much meets and exceeds all of the needs/uses for me and my family. Also, Fox has a great reputation in off road performance and racing, they have great customer service and also provide lifetime guarantees and maintenance of their products.
In the end, the Fox 2.0 has been AWESOME! They just eat up the bumps. And after speaking with Fox reps, I've decided that the 2.0 coilovers really give more than +2" lift to a Tahoe. They are designed for Silverados front load and that can be much more than a Tahoe's. The shocks come +2" out of the box and I actually had to dial mine back about 1/8". Though I lowered the ride height, I still saw +2.25" increase to the Tahoe's front wheel fender.
At the end of the day I only wish I had gone with the rear Fox shocks because then I would have had matching products front and back. But performance wise, I really don't think the rear shocks are that much different between Fox and Billstein. If my driving habits were different and I spent a lot of time on bumpy, gravel roads then the Fox rear shocks would probably be better.
On a side note, I have UCAs installed that are produced by Freedom Off Road. I am very happy with this product and their customer service. Speaking with them, they are now offering quick-lift front coilovers, adjustable front coilovers, and rear shocks. Their front coilovers look very similar to the Fox adjustables.
