thru-hiker here. I did it on $2k of credit cards, which is the least of anyone i met personally. a dehydrated meal with 350 calories costs $5 minimum, requires cooking (fuel cost/weight), and requires time/energy for your body to digest.
a soylent powder meal costs $2.
It does require you to go to the supermarket, quickly buy some ingredients, and mix them together.
Here is an example: You can just buy oats, skim milk powder, peanuts (a bit better if you buy them crushed, or crush them), raisens, and dehydrated fruit & berries. I also add almonds, walnuts, chocolate, coconut. It works out to b/w 25-50cents a meal if you buy at Costco, and is very healthy. You can add sugar if you want (I add a little, and a very small amount of salt).
You can also customize to your heart's desire. Replace milk powder with whey powder. Peanuts with almonds, flax for omega 3s, etc.
There you have it - The wisdom to outcompete soylent on price, nutrition, and taste, and all by a lot.
Not saying that's a bad option, just different.
The disadvantages to soylent are taste, chewing difficulty/calories, preparation, it stops up your digestive tract, and takes much longer to become usable energy.
Ah, now I know why it sounded good to me. As a Swiss we basically grow up with that stuff.
I guess it depends on what you mean by "better".
SAR is a niche within a niche. I can totally understand why Soylent is 1000x better than other options.
But most backpackers are doing it for fun. Reducing weight and space is great, but there are plenty of much more enjoyable meals that are only marginally heavier/bulkier.
At least for me, cooking a good meal before bed is my favorite part of the day. I'll happily carry an extra pound or so to make that happen.
TBF, a lot of purely recreational backpackers care less about the pleasures of life. The type doing 14 hour days and so on. But that's a small market, and all the folks I've met on trails who are doing that sort of thing tend to be pretty price sensitive. Young folks with few savings taking a few months off work don't have three months of Soylent money ;-)