Do annulments make it so that most people who could get a divorce/remarriage in a conservative Protestant congregation (apostasy, infidelity, abuse) can get an annulment?
None of these are grounds that would make a marriage null, they may be symptoms of a defect.
The word “annulments” is misleading, and is not the official term.
Going to talk first of Sacramental marriage (two validly baptized people who are free to marry who attempt to do so)
Remember, in other Sacraments the minister is the priest or bishop (except in emergency Baptisms and we shall leave that aside for now). In marriage, the two prospective spouses are the ministers, the priest, deacon, bishop, is there as a witness.
If at that wedding one or both of the parties had some sort of defect in their consent, a valid marriage did not result from the wedding. They may live together, have children, and only when the symptoms become too big to ignore are they made aware that they did not form a valid marriage in that exchange of consent during the wedding.
All the Church does is to review the things that led up to the wedding, the state of mind of both parties at the wedding, and determines if a valid marriage happened.
If they determine a defect, they issue a decree of nullity. It means while they attempted, the consent was not valid in some way.
This is a reason we parents need to start teaching our kids about what marriage IS from the time they are children, the world is going to tell them marriage is about romance and soul mates. That, as we can see, ends up with defective consent.
Romance is icing on the cake. Teach the kids first about what makes a proper cake.