I'm currently visiting San Francisco (SF) and experienced an opposite issue where GMaps reported cheaper and it ended up being more expensive. The BART train is a relatively fast, very cost effective way to get from SFO to downtown SF, Powell station in particular.
I was debating Uber at $30-$40, but looked at GMaps for public and it told me $2.50 to make that trip! Sure it takes 40 minutes with a bit more sketch, but I'm visiting, I'm willing and it's cheap.
Loaded up my Clipper card (BART's transit payment card) and went - ultra surprised when exited the turn style that my charge was $9.80.
The to/from the airport is significantly more expensive, which is understandable, but $9.80 vs $30 is much different than $2.50 vs $30.
Mildly frustrating, but in the end, not the end of the world.