It's torture because abortion is never a trivial decision to make - by the time a person has decided to get an abortion and not become a parent we should respect their wishes. If a decision has been made there's no reason to cause pointless emotional grief before executing the operation.

It is mainly so because of lack of education and emotional manipulation into mixing up human biology and human personhood. Heartbeat doesn’t make a person. It’s not even a requirement to be a person (people with continuous-flow artificial hearts lack it). The first specks of personhood appear a lot later in the process.

A normal sane reaction is “yeah, there’s already a working cardiovascular system, better stop it before the organism develops even further.”

This said, it’s an obviously pointless and harmful delay. There is no reason to check a heartbeat of a fetus if a mother decides she doesn’t want to carry it.