A passport card is $65 and good for 10 years. That's $6.50/year.
A Real ID driver's license driver's license in my state is $42 dollars more to renew for 6 years than a non-Real ID license. That's $7.00/year. It can also be renewed for 8 years for for $56 more than a non-Real ID license, which is again $7.00/year.
In addition to being cheaper a passport card can be used both as an ID and to show citizenship. A Real ID is only an ID.
Having to carry a passport card within the US sounds harder than just carrying my license. Especially when the passport card has all sorts of warnings about keeping it in the paper sleeve it comes with. It acts like it needs to be treated with kid gloves, and not just thrown in a wallet, like a license.
My wife, when she renewed her DL this time, got a drivers' license stamped "NOT FOR REAL ID PURPOSES" because she didn't bring in her identity documents AGAIN to the DMV.
Screw that. The passport lasts twice as long as a driver's license, and we're going to carry those anyway, so...why pay extra and have to remember all these documents? Passport renewal is easier.
But your comment about the need to get the passport in the first place and it being expensive is entirely valid.