That's a gross oversimplification and borderline offensive, to suggest that bus drivers are not victims of working on the 'front line' (often without adequate protection) but are victims of their own obesity... well, i'm not sure what to say to that. Thankfully i'd say the majority of people don't share your opinion on this.
Of course being on the 'front line' will increase vulnerability, just as it does for supermarket workers, NHS staff, home carers, royal mail staff, etc. However, whether you like it or not, there are numerous datasets available (I won't call them studies) that suggest a number of factors make susceptibility to COVID worse, such as those I listed (and there are more). As many bus drivers will fall into one or more of those categories, it cannot be denied that those are risks. If you consider mentioning potential risk factors, sometimes multiplied, which are prevalent in this particular group offensive, then what more can I say.
You might like to consider this: https://www.erinbromage.com/post/the-risks-know-them-avoid-them.
From what I've seen here, bus drivers are equally as well protected as supermarket staff (perhaps minus gloves, but with full-height screens and holes blocked off), and perhaps more protected than home-care staff (often reliant on just a mask, on the basis of radio reports) and non-isolation hospital staff (e.g. receptionists).
No, it's really not that simple. Buses that have been out of use for several months now require servicing, may require MOTs and any other work needed to bring them up to standard to return to service. Some companies have *hundreds* of vehicles off the road with most of their engineering staff furloughed - tell me how it's simple?
From what I have seen and heard, operators are moving vehicles and keeping them 'ticking over'. Indeed, in a two week gap since I cycled past, my local depot has moved every single vehicle that I could see front and back. I have, as said more than one, based my theory on any uptick in service coming in Stage 2, i.e. from 4 June, at the earliest, not immediately. Of course some days will be required, but a gradual increase in service should be linked to a gradual increase in vehicle ability. An operator who has literally just parked vehicles up for two months and done nothing to them surely opens themselves to questions.