why is that? Why can't you just use it in read only fashion?

No idea how it looks right now, but at some point Twitter started to block reading replies without an account. And sometimes it blocked even more, so you could not follow links to read.

sorry, maybe I wasn't clear. What I mean is that you can create an account to view posts and not reply, i.e. have a lurker account.

I tried to create an account but Elon banned it within a couple of hours for being inauthentic. Ironic given the large number of bots on the site

Can't you still read with a banned account?

I think this changed recently, but at least prior to that, when not logged in, you only saw the initial post and none of the replies.