In the North American context, "maternity care" would probably be understood as midwifery, which is not Planned Parenthood's main vocation.

That said, you're correct that Planned Parenthood offers many more services than just abortion, but the category they'd be in is "sexual and reproductive healthcare," not "maternity care."

Many advocates are pushing for "abortion forward" language to de-stigmatize the procedure, and (at least in Canada) some clinics are opting for less euphemistic names.[0]

0. https://www.cbc.ca/news/canada/abortion-clinics-language-1.6...

Because that's what they provide, and that's what they deal in, exclusively. Maternity care centers generally deal with other aspects of pregnancy, though some may also provide abortion services.

I got testicular/prostate cancer screening done at a Planned Parenthood (randomly, it was the closest place offering it) so I'm pretty sure they provide services other than abortions?

Sure, but that is not their primary focus, or historic mission. But what are you going to so with an organization founded by an out and out eugenicist.

Because "abortion" is a hot political issue in the US, and a word that pushes lots of people's emotional buttons. And because anyone using less-button-pushing words to describe things is a for-sure loser in the Darwinian attention economy.