The number of legitimate users on "not chrome, edge, safari, or firefox" is about 10% of the browser market. I don't know about you, but if I'm running a shop, and the whole point of my website is to make sales, but my front door is preventing 10% of those sales? That door is getting replaced.
You don't think the people actually running the shops, whose income depends on the shop, have thought of that and thus there exists a downside that more than offsets the upside?
The people running the shops aren't the people making the decision - Cloudflare is. The shop's only real decision is "use Cloudflare" or "die to all the attacks Cloudflare exists to prevent"
Then you get burglars in your shop instead of legitimate customers.
User Agents look the way they do because this is a recurring issue.
A browser without network effects gets blocked, they look for a way to bypass the blocking, then they become mainstream and now the de-facto UA is larger than before.
Why would you assume that the 10% of non standard browsers are going to buy anything?
Demographic is important here. If I was running a shop that sold software for Linux users, sure. If I'm running a store that sells pretty much anything else? I'm not caring.
Why would you expect people using non-standard browsers don't buy things? Presumably they still eat food, wear clothing, and enjoy hobbies.
I'd think that a non-standard browser also strongly suggests that they're a financially-comfortable middle-class individual, and quite possibly a whale with FAANG income.
Sure. If there was another place to buy a better door at. But if that door manufacturer's the only one that makes doors, if the door installer and door technicians all tell you that they can't or won't make another door for you, then you just deal. Maybe crank up the prices a bit to try to mitigate your 10% shortfalls.
The place where a business looks at that problem and sees money being left on the table that it can't live without and that it has no other way of making up for... that is a very narrow stretch, and only very marginal businesses live there.