The issue with the 20 week part is that the bill makes NO exceptions. If the fetus develops without a brain, the mother would still be forced to carry it to term, even if doing so puts the mother's health or life at risk, so that a brainless blob of cells can die at 9 months instead of 5.
The main goal, of course, is to make abortions very inconvenient without banning them outright, since that would obviously violate Roe v. Wade and would also piss off the financial conservatives who don't really like the social conservatives. As long as people with money still have access, they don't care if the poor get fucked over.