Why recently an increasing number of website isn’t supporting "request desktop site" anymore?

Recently I more and more often, access websites via my mobile, just to realize a certain feature has no (more) support on the mobile version of that site. So I request the desktop site (via browser functionality). But even then, as soon I click on any link, the URL changes to something like m.URL.TD or having somewhere in the URL a .TD/XXX/mobile/.... So my impression is, the sites providers actively want to deny desktop site access from mobile devices. Why is that so? Especially since most of the time, I am getting denied access to specific features I intend to use this way. And that way I feel often very dissapointed in regards of user experience not to say sometimes I get even mad about this logic, as I can't see, why a site wouldn't allow a user desktop access, where the user actively presses a button representing "Hey, I know my experience using this site as desktop version despite being on a mobile device might give me a bad experience." So the experience of being denied getting that explicit requested desktop site is (at least for me) even worse.

Ideas I have come up with, why this could be done:

  • The site has an App, and wants to enforce the user to use the App instead.

    • But not all sites I noticed this recently have even an App.
    • Also, I wonder, is it that important, that their App is being used that they risk users stop using their service at all?
  • I.e. my bank denies it. But as soon you request a desktop site you get an information that continuing in desktop mode from mobile device is not supported by them, due to security risks. But you can just ignore that info and you remain on the desktop site. I am fine with that.

So given the above bullet points, I don't really can see that this justify taking away the users agency.

So what am I missing? Or what other reasons are there that I notice this behavior recently more and more often?