Similar thought, and Google acquire does seem like a plausible route. However, checking over on Play [1] they've apparently got In-App purchasing at $3-50 and 300+ cities and 1000+ transits that let you buy fare and passes. Seems like they're already making money anyway. Teams pretty extensive though, so it does look like a lot of annual money's probably necessary to float. [2]
They also partner with transit agencies where the transit agencies pays them to upgrade everyone in the region/system to the premium offering, and the transit app becomes the official app for that transit agency.
I never paid a single cent in this app and yet the app is perfectly enjoyable. I've used it since 2019. What's wrong with freemium? I don't need extra features and the free features are good enough for me.
The thing I specifically paid for (that Google Maps doesn't seem to offer) is answering the question "what transit lines/stops are nearby and how soon will a service arrive at the stop?" Last I looked they limit the number of lines shown in this way for freemium users.
If you're just putting in a destination and getting a fastest route (much like you'd do in Google Maps), then I didn't see much benefit to the premium version.
[1] https://play.google.com/store/apps/details?id=com.thetransit...
[2] https://transitapp.com/team