I've noticed a thing that AI always gets far more better starting position than me, they will always have more resources than me, I have to reroll so many times to get a decent start. What's up with that?

What difficulty do you have the playthrough set at, and what's the difficulty of the AI opponent? They're separate entities and (along with the set speed of the game) can affect how fast the AI constructs its civilization. I've found on Humankind runs that Expert AI's will have their culture selected and outpost in an optimal location before the player can even begin exploring the map, and another community member, who used a mod to spectate the game, found that the AI is primarily focused on constructing districts > infrastructure which affects the raw level of resources they have access to (due to them expanding districts and territory much faster than the average player).

This may help too, it's a link to the Humankind wiki on bonuses given to the AI or player based on the difficulty of the match. 

I don't that difficulty matters that much, it's just they spawned surrounded by a lot of resources, while I get little to no resources around me

I just keep restarting until I get a decent location. That can take anywhere from 3-5 tries most of the time. It would be nice if a shortcut such as Ctrl-N was available. My current game I have more resources in my start location than I can easily extract. I didn't even take full advantage because I wanted to start as the Bantu.

It's really easy to trade for resources in this game as long as you're not at war.

In my latest game I spawned right in the middle of resources. And it was the only clump of luxuries on the continent.

I'd say it's random. The main 'issue' being that luxuries clump together. And if there's a lot of land, there's a lot of land without resources.

Very true about the clumping, As for buying resources, I've found trading for resources much more expensive since the latest update.