How often do you get Prolific studies?

So I created a Prolific account since I saw so many people here talking about it.

Thing is, every few days I get an e-mail that says "new prolific survey from Jim".

As soon as I click on it, it is too late and it reads "study no longer available".

So I'm a bit perplexed. Are the studies that few and far between and we only have a super short period of time to click them? How do you guys get all of these surveys?