When twisting the lever, the catch only has a range of motion of around a fourth of an inch, and high school and college aged children tend to warp these cases (particular down at the bottom when all of the smacking against bump-downs occurs) more than that amount of tightening range.
It's a combination of awkward/large size/shape, step-downs, weight, "hurry up, son", "it ain't mine", and (perhaps...??) just a bit of alcohol and cannabis mixed in for good measure.
Some of these children might "work out" in a gym (etc.), but that's not going to give them "mechanic-like"-strength in their forearms, wrists, fingers, or the (not the ones that they typically exercise on workout machines) certain pectoral muscles required to squeeze the bottoms of those cases back together enough to hook those butterfly latches over those catches and turn the levers.
As sort of a joke, after repairing those sousaphones I always latch those bottom latches,
because I know they're going to work their tails off getting them back open again. With the smaller cases that fit JP (which are knock-offs of the MTS with the same butterfly latches), children are still going to warp the cases - but the span from end-to-end (as the JP cases are only large enough to fit King, and the JP are modeled after King) is shorter, thus the warping tends to be less (arithmetically) and those butterfly latches - then - can still catch those hooks (without herculean efforts) and be latched.
The regular (marketed...not "Conn-Selmer" sold) MTS latches (square drawbolt - similar to some found on some Yamaha cases) are OK. Yes, they tear up, but they're also available to buy, and a hammer, chisel, pop rivet gun and some long medium-size peel rivets are all that are needed to replace the lower "business" halves of those latches pretty easily...and those latches have a lot of range, and can still catch the top halves of the latches on abused molded cases.