Let's not pretend Arriva are some kind of victim here, the fleet issues are a result of mismanagement in the DB era resulting in a vicious circle, unreliable buses lead to unreliable services which puts passengers off, but that's not all, the buses are truly filthy, the seats are stained and ripped, floors, walls and windows and grab poles all have thick layers of visible dirt that have built up over a long period...
Giving the fleet a deep clean is a cheap and easy way of improving customer satisfaction, but it just doesn't happen.