You would be surprised how many people actually keep toxic people in their life. I do it a lot. It feels good to have someone pay attention to you, even if the attention is negative. At least when you are being hurt, people are paying attention to you. When you are being ignored, you are all alone.
I'd like to say that, as someone who has gone from having toxic people in my life, to cutting those people out and being very lonely, it sucks at first, but in my experience, being lonely isn't as bad as being degraded by forcing yourself to hang out with bad company, IMO. While it's healthier to just have good friends, out of the two options, being alone definitely has more benefits than being in the company of people who don't respect you.
Not telling anyone who doesn't know if they are able to handle it to cut out toxic people when they aren't ready, but as someone who has made that leap from having toxic relationships, to having just a few relationships because only a few people in my life weren't toxic, being lonely but safe, and strong, and respected, feels nicer than being hurt.