Yeah that's is annoying. A lot of those people generally have an auto follow set up that unfollows if you don't follow back, even within hours. Or simply follow you in the hope that you'll follow them, then when you do, their jobs done so they unfollow & presume you'll never notice. You can get separate apps that tell you who've followed & unfollowed for people who're bothered & want to unfollow those people back too! Haha
I only ever follow profiles I genuinely like the look of. I never do follow-for-follows & I don't follow people just for the sake of it if they've followed me. I'll check their profile out first.
The sudden increase in spam comments at the minute is driving me pretty crazy though. I'm reporting a handful a day. Not just on my acc but other people I follow too.