Everyone bowing down to mangadex is not good at all, and anyone is allowed to have their own site if they want. You are just being entitled.
Choom, when the other sites do the right thing and direct to official sources/services, then you'd be right about entitlement cause I like dex's format, but with most of the scanlators I've seen, most haven't done the done bare minimum, and a lot of them likely won't as they're in it for qick cash, ala traffic on their site.
Even the "bowing down to mangadex" is flawed because dex was trying to cut down onscalpers/con artist, bad scanlations, outright piracy, and othe malpractice. I think it akin to a communal pirate bookstore, everyone knows it's "extra-legal", but we'll work with authorities so the whole bookstore doesn't get shut down; for some, it's a bastion from the malware-ridden places (that could be scanlators or aggregators)).
You're also right that they don't have to post it on mangadex, but it's more guaranteed that certain projects, such as old obscure works, likely won't get the same recognition and'd die with that scanlator. Some of the series I've read, I also picked up official releases (I'll conceitedly believe I was the main contributor to the Ragna Crimson anime), Ikigami, Angel Densetsu, 20th Century Boys, and Akumetsu.
After mulling it over, though you said it in irritation, I'm likely entitlement but not without good reason. I've had more positive experiences with dex or other aggregators, and not with scanlator sites and the petty bs that goes within those circles (insert GOW Atreus talking down to Brock and Sindri here)