How is a cervical check different from sex?

Ok so like legit question....why do they delay cervical checks to the final weeks and ask permission bc it’s such a risk of starting labor? And yet sex is ok???? This has always boggled my mind lol my dr warned me and asked my permission if I wanted the check done at 36w 4d bc it could get things started but how does the dr putting a couple fingers in there and touching the cervix for a few seconds pose such risk but a big dick jabbing it for 20 minutes or whatever is totally fine and safe?!?! Hahahahah sorry for the tmi but out of curiosity...wtf is the difference?