mobile web: why recently a growing number of websites no longer support "desktop site request"?

Recently, more and more, I access websites through my mobile, only to realize that a certain function does not have (more) support in the mobile version of that site. That's why I'm requesting the desktop site. But even then, as soon as I click on any link, the URL changes to something like m.URL.TD or have a place in the URL to .TD / XXX / mobile / .... So, my impression is that site providers want to actively deny access to the desktop site from mobile devices. Why is it like that? Especially since most of the time, I am denied access to specific functions that I want to claim in this way. And in that way I'm often very disappointed with the user experience, not to mention that sometimes I get angry about this logic, since I can not see why a site does not allow a user to access a desktop, where the user actively presses the button that represents "Hey, I know that my experience using this site as a desktop version despite being on a mobile device could give me a bad experience". Therefore, the experience of having been denied that explicitly requested desktop site is (at least for me) even worse.

Ideas that have occurred to me, why this could be done:

  • The site has an application, and wants to force the user to use the application instead.

    • But not all the sites that I noticed recently have even an application.
    • Also, I wonder, is it so important that your application is being used to prevent users from using your service?
  • That is to say. my bank denies it But as soon as it requests a desktop site, it obtains information that it is not possible to continue with desktop mode from a mobile device, due to security risks. But you can just ignore that information and stay on the desktop site. I'm fine with that.

Therefore, given the previous points, I really can not see that this justifies removing the user agency.

So, what am I missing? Or, what other reasons are there for me to become aware of this behavior recently more and more often?