At the end of the day, bus companies are just that - companies. They are commercial entities that look to make money. They target their investment in order to get the best returns, which is what their shareholders also look to achieve. In this instance, bus companies will invest in those routes and areas where they can achieve the best returns, which makes absolute sense. This is either in terms of commercial growth, tied contracts (e.g. University services, Park and Ride etc), council tenders (much less common now) or as part of a quality partnership - all of these will have a financial benefit to the operator.
Stagecoach were very clever in the past by being able to cascade vehicles from London (when they were relatively standard) or from Manchester into less lucrative territory (i.e. the initial balance sheet "hit" was borne by the most lucrative operations). This allowed relatively modern vehicles to be cascaded and so improve services so that, in some cases, they were able to then sustain new vehicles. There have also been examples of OpCos justifying new investment for other reasons (e.g. North Devon Wave).
It all boils down to the OpCos (of any firm) creating a business case to justify the investment and being able to stand behind that case. Imagine if you get a 2million investment in new vehicles and it DOESN'T deliver the returns and then, as the local MD, you have to justify that?
There are, of course, some initiatives that come from the centre. OpCos may not particularly want that investment - how the First FTR concept got signed off, I will never know? Similarly, the Ashford minibus experiment may also have a certain amount of leeway from Stagecoach board.
It's not like the olden days when bus companies allocated a new bus to some rural depot just because it was a "nice thing to do". The last Bristol VRs delivered to Crosville were delivered to Llangefni, Aberaeron and Aberystwyth..... Mental!
