
As many people have mentioned, there is no reason why insurers could not
offer a contract without abortion services for a different premium.
The problem is that there is no guarantee that this premium would be
lower for those who chose this type of contract.  Although you are
removing one service, that may have feedbacks into other types of covered
care which results in a net increase in actuarial costs.

For an illustrative example in the opposite direction, it may be possible
to ADD services to an insurance contract and REDUCE the premium.  If you
add preventative services and this reduces acute care use, then the total
premium may fall.