It's the reliability of a lot of services that's killed bus use tbh especially in Glasgow. The train being decent plays a part too but if the buses were even remotely reliable even outside of peaks they would be more used.
I can get the 1s, 2 and 6 from 3/4mins away from my house and the 3 and X4 are about 10 mins away yet out of them only the 1C and X4 outside of peaks are even remotely reliable. Very often ends up 3/4 2s and 6s within 10mins due to bunching up both ways. Feel for drivers in that situation too because they take the worst of the blame from customers but it's 100% not their fault.
It might be costly but adding back in more recovery time and more drivers with more buses might be the only way to stop the decline going forward although a lot of what I read and hear from people is that they're done with buses for good unless the train becomes a disaster or car cost goes up so massively they can only afford bus.
Also all the depots had timespare (drivers sitting spare) throughout the entire day. That was cut 10 years ago and only in mornings there is timespare usually 5am spare. Come the afternoon/evenings there’s nobody spare. So if a driver goes home sick or has extended meal break so be it the bus comes off the road. Back 10 years ago if a late shift collapsed, bus broke down or extended meal break no bus would need to come out of service.
Plenty of people are done with the bus now. Most places in Glasgow now wait longer for a bus compared to 10/15 years ago as many services cut. If 2 are traveling together over a short distance then getting a Private Hire could also be cheaper and drop you right at the door of your destination..