There's some fair points being made and it's not an exact science.
Firstly, what is the pattern of bus services. I know of few bus stations (Swansea, Preston, spring to mind and possibly a few others) where high frequency local buses use the main bus station. In most places, such is the frequency, roadside stops are generally used for both practicality (hard to accommodate such movements in bus stations) and also reflecting the shorter periods that passengers need to wait.
This is also helped by the route network with cross town/city routes in many places. However, passenger and non passenger surveys have consistently highlighted that a decent place to wait is a key consideration. We wouldn't think of having a reasonably sized town not having a railway station with reasonable facilities (information provision, toilets, shelter, etc) but seem to be ok with it in the UK especially where we have a greater reliance on inter-urban bus services with wider headways as train services no longer exist.
Also, we have the issue of road networks with some towns have traffic management schemes that scatter services across town centre. Hence, a central point to wait does make sense and in most towns and cities (if not all), the single busiest traffic point is in the centre and usually by a huge margin.
To highlight an example.... Bristol. It has a comprehensive set of city bus routes. These run through the centre of the city (though relatively few serve Temple Meads - generally only those routes that run across the city and use the A4/A37 to the south east (though Clifton and UWE do get specific route extensions). A terminal there could be formed by sacrificing car parks and it is near some of Temple Quay employers and the new arena.
However, it is still in a peripheral location. It is a) at least a 15 and nearer 20 minute walk from Broadmead - a bit shorter to Cabot and bit further to Millennium Square b) it's more than a 5 min extension on the bus reflecting the issues with Bristol's road network (as designed for the car in the 1960s), and c) we're not getting a tram system but instead a set of dedicated busways (not guided).
Therefore, should you wish to commute or visit Bristol from the various dormitory towns like Keynsham, Nailsea, Thornbury or Yate, train travel is an option but it is convoluted. For example, to go from Yate to Bristol is about 45-50 mins on the bus. The train is quicker but to save 5 minutes, a single mode journey would be turned into a three mode journey - two buses and a train in the middle. Sadly that's a pattern replicated across the country; a reflection on our lack of metro and tram networks, a legacy of Victorian train engineers? Very possibly but a fact nonetheless.
Of course, it would be fantastic to have better public transport, metros and trams in our major cities and services at such a frequency as to not need bus stations. However, the reality is that we don't have that. Bristol bus station provides a modern, clean environment that is dry and safe, with cafe and shop facilities, toilets, information etc. Just what you'd expect from modern public transport. Compare that with Cardiff. It had a bus station (now lost to development pending a smaller facility appearing) and where do I catch my bus from....one of five different streets across the city centre!
Regarding Accrington specifically, the market stops were definitely convenient for the main shopping and commercial areas. Did it need a bus station? Possibly? However, will it be an improvement..... I compare the old bus station in Nelson with the new one. Like night and day, almost literally given how dark the old one was!!
There are some really glaring examples of towns that really should have better facilities and they could be co-located with rail stations. Why shouldn't Scarborough not have something akin to Bath's bus station, near to the main shopping streets and next to the rail station?
These things are never binary, black/white, good/bad. There are places that perhaps have bus stations that seem incongruous by their sophistication and scale (e.g. Ossett). However, having spent fair chunks of the last 30 years waiting in the rain for buses, I can vouch for the relief of having decent facilities in which to contemplate life!!