The killing off of classic bus company names, no matter what their local appeal, can be largely placed at the door of London investment companies and advertising organisations. It is the same rationale that has led to local radio station names being replaced by Capital, Greatest Hits Radio etc. Those investors and advertisers find it impossible to understand that a brand they don't see around them in London could have any commercial value. It is a very insular, short-sighted approach.
This has gone on since time immemorial, not just in the modern day. Remember that, in South Wales, firms like Rhondda, Western Welsh, United Welsh, Red and White were all lost in the 1970s. Think of all the municipals that disappeared in Greater Manchester under the SELNEC name, or the other PTEs? In the early days of the NBC, there was a lot of rationalisation with Alder Valley, the loss of Wilts and Dorset and Midland General (and the ones rolled into Northern), and the introduction of the National coach network meaning historic local names were either lost or relegated to a small fleetname. Go further back and you have White Rose of Rhyl being consumed by Crosville.
It has always been the way of the industry. Yes, there's the stock market profile as a factor, but often, it's just the simplicity of not repainting vehicles, savings from consistent branding etc
Of course, and this could almost be a thread in itself, is having "local names" that are nothing of the sort. Lincolnshire Road Car was a classic example with their Newark depot (which led to a short lived East Notts fleetname in the 1980s), but what of National Welsh in the Forest of Dean (again later remedied) or indeed, Bristol on buses that were nowhere near Bristol!
Ah ok, thanks. Stroud Valleys is the name I was familiar with when I occasionally visited the area in the early-to-mid 90s. ISTR it was the Cheltenham and Gloucester company which had four separate brands for Stroud, Cheltenham, Gloucester and Swindon.
When Bristol Omnibus was split in 1983, the four depots that formed Cheltenham and Gloucester got those local fleetnames as well as gaining new liveries (City of Gloucester = Blue, Cheltenham District and Swindon & District = poppy red); only Stroud Valleys retained leaf green. However, the remaining Bristol Omnibus gained local fleetnames with the return of Bath, and the introduction of Bristol Country (for the Marlborough St depot ops), Citybus for Bristol city ops, and Weston and Wells, until it was split again with Cityline and Badgerline.