Giving someone a bus pass doesn't help if there are no buses to use it on. It's chicken and egg really. We need better bus services AT THE SAME TIME as your bus pass proposal, for it to work.
It would only work on, say, a bus route where there's an irregular or infrequent service, i.e. hourly or two hourly, or no bus in the evening or Sunday, etc., where there's be an increase in users on the existing sparse service to give a "nudge" to the bus firm that there may be the demand for a more frequent service.
It does nothing at all where there isn't currently a service at all,
That's the problem with public transport. The routes/services etc are all historic, so if number of users on a route fall, they reduce/remove the service. It's nigh on impossible to get a new service introduced.
We had a huge out of town supermarket/retail park built that was nowhere near a bus route - it took a whopping 20 years before a couple of local routes were "tweaked" to include it so that locals without cars could actually get to it without relying on lifts or taxis!
Same happened with our nearby city's park n ride scheme which didn't go anywhere near the main hospital for our entire county. It took years to get them to change the route to include the hospital!