It's a great idea in theory, but the bus service here is dominated by one company that has underperformed for decades. Not only that, but they have a history of pushing competition out where possible, and reducing routes to overload other companies that move in - so there's that problem.

Politically, Bristol is quite strange. Lots of corruption, lots of green ideas, but lots of problems that need tough solutions. Around two decades ago we were sick of our council being so corrupt, so we voted for elected mayors like London. The two mayor's we had were both corrupt - one syphoning off green capital money to his family, one pretending to build an underground subway and an arena while taking kickbacks from YTL and achieving literally nothing. Both mayors touted a subway, and one funneled tens of millions into...another set of bus routes now controlled by private companies. The second spent a decade of terms pretending to build a subway, and achieved literally nothing. We now voted to get rid of mayors, and the council are shit again.

To then answer your question - all of the above and more. The bus service would probably need to expand by 3x overnight to be reliable, it would also need additional routes AND to somehow not get caught up in the horrendous traffic in the city. The buses have been so bad for so long, with so many broken promises, that many locals just drive or cycle, because at least that way you'll get where you need to go on time. It's probably the one thing that everyone in Bristol is unified by, and any talk of trams, subways, etc are all met with "you can't even run a fucking bus route, how will you manage that".

To cut my rant short, Bristol is too big, too expensive, and too poorly connected to make commuting possible. It needs a bold decision to be made, rather than giving First's shareholders some more money.