Amazon Prime is particularly heinous about using dark patterns to confound users into risking forgetting but ultimately you’ve already paid for the month, year
I can confirm this to also be the case with most streaming giants plus the less-giant Shutter
Edit: comments have pointed out some notable exceptions such as services through Apple and HP Instant Ink
There are exceptions, but yeah the pro move is to immediately unsub as soon as you sub if you’re not planning to stick around.