And it is a bad design decision that is universally hated by everyone.
It is a straight up bad UX and not user first, and the owning team defends it because they don't rely on common sense.
Of course, if you put login prompt anywhere, you would get at least some logins or signups (at least 1).
Twitter had this issue before where they didn't allow non-logged in users to browse twitter home at all by showing a non-dismissable login prompt. It took Jack Dorsey to come back and change that in 2016.
But yeah sure the non-dimissable login prompt on the search page is great. Hahaha
This is how bad product management at twitter is