IF you have ever had to try to unblock a plugged waste line in 96 degree heat inside the cramped space that you have to work with, you'll agree that making someone us a little "bag" isn't so bad ;^)))
We used to charter our first boat out. On time it returned "crammed-up". The only thing worse than having to deal with it, is to try for two hours to clear it (with a toilet full of stuff that "didn't get out", and then not exceeding. I had to call in a service to take things apart because I didn't have the stomach, time, or nose to keep messing with it. The culprit was some combination of tampons, and packing in "home" toilet paper. I ALWAYS provided high quality marine TP for the charters; and, I admonished them to just use the TP we provided; put nothing else in the toilet that didn't come naturally out of your body.
In parts of the world (including South America) where sanitary lines are smaller, it is not unusual to have the local practice to use a little "bag". Bidets have clothes that are stored in bags (and washed and reused, in some cases).
P.S. -- I haven't had that happen again on our boats over the last over 35 years of sailing. We just use Sealand or West Marine TP and have never had another issue.