It's unlikely ads would ever actually fund any meaningful real world product or service like public transport. The most they can fund is some crappy apps, websites and digital platforms, and most of the time they can barely do that.

It's only a matter of time before our ad-driven tech economy pops when they realise how much fraud is committed by the adtech companies, how little return these ads really give, and peoples susceptibility to ads further declines, causing them to exhaust even the most invasive and penetrative advertising techniques.

A nice idea I saw was a service where you can get a free/discounted public transport ticket for doing some squats or other exercise in front of a machine. Something like that would shift a lot of money from handling healthcare for the inactive over to providing free public transport.