Why does he keep asking me out and then says he doesn't have time? (casual sex)

So there's that guy I met once and now we keep texting a lot. (We weren't talking a lot when we met though). We both are not interested in a relationship but we want to have casual sex. The only problem is, that he always asks me if we wanna meet for sex,we chose a day, then he backs out by having a cheap excuse. He is always the one asking for sex, it's not me (I kinda just trigger it). Why does he keep saying he doesn't have time then? Why does he keep asking me if I wanted to meet him then?
He is definitely NOT a shy person, so there's actually no reason for him to be afraid or nervous ...he also gets a lot of girls to sleep with him according to what he told me, I have no proof though.
Another problem is: The only thing we really text about is sex. He never answers any other questions I ask, like what he's doing right now,...etc. Also, he takes really long to respond to my text messages most of the time or doesn't respond at all sometimes and I'm sure he does check his phone at least every hour. Is there a reason he doesn't reply faster? Is it a thing guys do to keep girls interested? It's mostly me who texts him first and I kinda feel a bit awkward texting him so much...I don't want to annoy him..

You are willing for him to use you and at the same time you're complaining about being used. That's like hitting yourself in the head with a hammer and complaining that your head hurts. :-)

It sounds like you feel disrespected. You say, "I don't want to annoy him," but *you* sound quite bothered. It's as if you're starting to put his feelings above your own. Casual or not, you have to decide if you want to be in any kind of "relationship" with someone when it makes you feel like this. Plus, the point of having a fwb instead of a bf is that you get to avoid the emotional crap.

I say don't text him anymore. Walk away and find what you need elsewhere. What's the point of having emotional crap with an fwb without the sex?

It sounds like he is playing games,
Maybe he has some kind mental disorder.
That is strange, but yeah everyone is right here.
So go about your own way and drop him.