i hate it cause i don't get paid for taking care of the p switch. i got it to bed on time and with no issue and you're still not gonna pay me? this is highway robbery
Jokes aside, apart from all the usual reasons, being that it's not very creative, engaging, or fun, I think the big reason is that it's kinda limiting and very easy to go wrong.
Mario has a few abilities that're straight up not usable when carrying an item, meaning he has to use maneuvers just to do certain things. He can't spinjump unless he kicks the item upwards and then grabs it in the air while he's doing the motion. He can't climb walls or vines without doing a similar thing here. He can't spin with the cape, and he can't shoot fireballs with the Fire Flower due to holding the item having the same button as those actions.
While Yoshi can hold those items too, Yoshi will also eat them after a matter of time, which at best is incredibly annoying to keep track of and manage (he's about to swallow that key, spit it out on safe ground, lick it again, rinse and repeat until you reach the keyhole/correct p-switch position), and at worst can pretty much guarantee that you need to die and restart.
These are normally pretty annoying on their own, but they're negligable. They don't become genuine problems until you actually have to start carrying them throughout an entire level. It's got similar problems to escort missions, which, again, can be done well, but it all comes down to execution (and for escort missions how reliable A.I. is, which is kind of a crapshoot).
Of course I'm a
FILTHY CASUAL who hasn't played a bunch of Mario World ROM hacks, so I'm probably not as experienced to give a surefire answer (since I can't say I've played a lot of levels that have item baby sitting, and if I have, I probably forgot about them lol), but that's just how I see it.
Also while writing this post I literally got the tip at the top saying "avoid using item babysitting", which really says it all, huh?
PFP by
Empathic-Nooks on Deviantart. Check em out!
Hey check it out I made a level that got 104th place (wow he sucks!).