I seriously doubt they removed seats because people were sitting on them.

More likely it was costing too much money.

At least in my city, some people don’t just sit on a seat (or sitable landscaping feature like a low wall). They eat on them, drink alcohol, leave behind food scraps rats eat the food, bottles get smashed, some people even go to the toilet next to the seat, etc. And yes - there are rubbish bins and toilets nearby.

Sometimes it’s worse, bloodstains, fights, etc.

The only parts of the city that have seats are cleaned three times a day and heavily policed with plain clothes officers on foot patrolling the area 24/7/365. That cost wasn’t necessary 10 years ago but it is today. We could go into why but that’s largely irrelevant.