+1 hi, menstruating human here. I don’t represent all of my gender, but can say from experience that yes reusable options aren’t always the best option. You have the issue of needing (ideally) clean running water & clean hands each time you empty the cup... maybe more relevant to the discussion than the sustainability argument. (Try getting your period at Burning Man.) Also many women never use menstrual cups because they can be difficult to insert and remove.
While TSS has ceased to be common in most places, our education about not leaving tampons / menstrual cups in for too long likely has a lot to do with it. If you have limited access to tampons or necessary resources maybe you leave them in longer than you should, harboring bacteria, etc. So idk, I care about sustainability too it’s clearly an important issue, but so is gender equity & women’s basic health & access to education...
Yes big tampon is really a thing (more about flow than size) but also so are slender/junior tampons for teenagers.