I very much desire and enjoy sex, I have a high sex drive and am quite kinky. I've had good sex with strangers or people I've hooked up with once or twice, but I've had amazing sex only with people I've had a strong emotional connection to. A part of it has to do with repeated encounters: I am more likely to have more sex with people I feel more connected to, and the more sex I have with them, the better it gets as we get to know each other's bodies more, and get to explore and try more things. Greater emotional connection also means I will be more relaxed, which frees up my mind and body to experience and share pleasure with my partner.
I also have generalised anxiety disorder, and am quite introverted and easily worn out by socialisation, so I strongly prefer to spend time with people I already know and trust in all contexts, not just sexual. This is exacerbated by the fact that I have quite a few kinks and fetishes, and I often get very anxious as to whether the other person will also enjoy them, or if they will judge me harshly because of them. I also get scared about seriously harming my partner, or crossing limits/boundaries, the risk of which is reduced as we establish solid communication and trust. With hook ups and new people, you can only really do the generic stuff unless you've talked about what you want to do and limits etc. extensively beforehand, and while non-kinky/BDSM sex can be good when done right, it often just bores me.