It's because they get paid way lower than minimum wage, so they have to rely on tips in order to like, live.
Depending on the state, a base pay for servers may be less than $5 an hour without considering tips. And the problem is tipping is still not "formally required" or anything like that, so you've got some scumbags that still don't leave a tip (essentially wasting the server's time). Because a tip isn't 100% guaranteed, of course servers are going to be checking in on you regularly and making sure things are taken care of. Scratch my back I'll scratch yours. Maybe it feels forced, maybe it's not, but it's their job at the end of the day.
With that said, the system in the rest of the world is way better, and I think America should do away with tipping altogether. Pay the employees a livable wage, and the number customers see on the bill is the number they actually pay. Some restaurants have already begun doing that on their own, but they're still far and few between.
Sorry to ramble on like that. I can understand if the regular attention from the server feels a little unusual. But I just don't feel like that's a fair reason to not dine out.