It's not millions of people, most people get Real ID. In the context of airport security budgets, it's not that much. And it's used for hiring the additional staff required and putting together the identity verification systems they use.

Assuming 100M "classic" ID checks (being generous): congrats, you just paid for two days of running the military!

But everyone would have to take advantage of that benefit not having ID have with themselves.

The roughly 7.6 million CLEAR members paying $209/yr grosses them north of $1 billion/year. It's not hard to see why TSA wants to get in on it.