All gyms have raids or is it RNG?

Hell people from big cities who swim in pokestps and gyms,
I wanna ask you something. Are you noticing if all the gyms have raids? Or they are always in the same gyms and some don't ever get any?
My city has the enormous amount of 1 gym. No raid until now.
The colest one is 45km away in a neighbor city. And the gym there had 3 raids in the last 24 hours.

Hauahauha. Oh my god. It was like Niantic was just waiting. Right before I post this a yellow egg level 4 raid appears. In two hours I will fight my first raid! Wish me luck guys!
(Where the hell I'm gonna find people to defeat this bastard?)