Yes, and that's one reason why costs have ballooned so much, the need to subsidize people who didn't pay while they didn't have a condition and now do. The temporary plans aren't even necessary, if you can wait until the next regular enrollment period.

The ACA originally tried to hide that vulnerability by making insurance mandatory, then it appeared when that forcible mandate was repealed.

Edit to reply to the reply: Right, it's not insurance. Insurance is pooling risk. If you wait until the risk event has already happened, it's not insurance, it's just paying your own costs with extra steps.