I labelled it "bloat" because a "basic" dice roller has extremely limited usage for an app designed to appeal to so many different systems. In fact, MT might have native support for more systems than any other VTT out there--you just have to use basic macroscript to tap into it (which I agree is not for everyone). And while, clearly, there is demand for something basic given the number of drop-in rollers that have been made over the years, if only a small percentage of users end up using it, that's the definition of "bloat".
That said, I've always wanted MT to have in-app links to some drop-ins so people could more easily get them into their games (even if it was via something like the "Add Resource to Library"). If you could go to a section that said "Rollers" and have easy access to all the rollers I mentioned above, with an easy download, I think it would be much better for new users.
Taking a deeper dive, I think one of the reasons MT doesn't have much in the way of a UI dice roller is because "in the beginning" there was a sister tool called (you might have guessed) "Dice Tool". https://www.rptools.net/toolbox/archived-tools/ And I think there was some early resistance for MT to do things that the various sister tools already did "better" when there were so many other things it was building out... and I also vaguely remember lofty plans for integration of the various tools that just never manifested. Eventually, MT's capabilities superseded the abilities of the other tools and they fell to the wayside... but, for better or worse, most of that functionality came in via macroscript (and dropins), not shiny integrated UI elements.