They have descended into a First style rabbit hole of under-investment and retrenchment, long before Covid. The age profile of the Arriva fleet was pretty decent, especially with the investment around 2010-5 in order to be compliant with DDA legislation or, in the case of the North East, a continuing rectification of a lack of investment between 2001 and 2007.
With
some similarities with First (in which UK Bus became a cash cow to help pay for Laidlaw), Arriva has been starved of investment as DB's debt pile has grown (and long before Covid appeared. This article from 2019 has some more detail
https://www.dw.com/en/germanys-deutsche-bahn-3-billion-short-on-cash/a-50412978 . That has led to unrealistic return expectations and so not hitting budget is now seen as a reason for limiting capital spend and protecting what cash they have. Aside from a few batches for the provinces (such as Yorkshire Streetdecks), there's been very little other than to London for contractual requirements, for the last 4 years.
It's been like that since they closed Chatham (Luton) depot 20+ years ago, and of course, exacerbated by low floor/DDA resulting in longer wheelbase vehicles to retain capacities. Not certain how much room Maidstone depot has but echoing the question by another poster, you wonder if the putting of TW depot onto the market is a reflection that they will simply run the 6/7 from Maidstone and simply have an outbase in TW for what's left.
It had been 20 years since I'd spent some real time in the area and I remembered there were always a fair few local operators but it feels that Arriva are much less dominant than they ever have been. Perhaps it's subconscious negative confirmation bias but just felt that way?