I really feel for you, this seems like a no-brainer, but my DHs insurance (which our youngest is still using until summer when she ages out) has always disallowed maternity benefits for dependents. My school insurance (when we used that) also disallowed it. It’s wrong, but it has been the norm most of the time we have had medical insurance.
Maternity coverage wasn’t required on individual policies before aca, and was excluded from dependent the coverage for group policies to keep costs down. My kids had individual policies and it was excluded, very clearly, from coverage. Since they were 10 or 11 at the time, I didn’t worry. ACT required it on all individual policies, and for the primaries on group. Some other things are not required for dependents on group policies either like mammograms even though they are required to be covered for primaries. So, this was not something removed from policies, but never included in the first place.
Most states have some program for pregnancies not covered by private insurance, either chp+ or medicaid.