I think there is also a chance people can make it rain themselves right? I am not really knowledgeable about the situation at all but I think I have saw people (not pd people but literally gamblers) giving out free money to people on chat after a big win, don't know if those are still pd people but looked like it was just gamblers who got too excited about winning a big bet and just wanted to share the money with others as well.

So, the chance of getting a random rain (free money) is not just limited with primedice employees giving out rains to you but also other people doing that as well, so every single day there are tens of rains going on and even though you may not get one for days in a row its inevitable that you would miss out on rain if you are constantly there.