From what I can guess, ex council houses are always in what are referred to as "less desirable locations", simply because a council estate is never a desirable location.

These then will just about always be worth less than the equivalent private built house. In a way this isn't logical, as I know streets of ex council houses which are fantastic built houses, large gardens and the areas they are in are very quiet with no trouble, however...........there you go.

So, one criteria for buy to letters is that the properties have to be affordable for them to buy it. Ex council houses tend to be affordable in the main - so are targetted by buy to letters.

And that probably is it. It's a nightmare where these buy to letters are buying up starter and second homes, and turning respectable neighbourhoods into areas of transient population, breaking social cohesion.
You can be absolutely sure of one thing - the buy to letters won't be living next to the sort of mess they will inflict on others.