Because some TV producers share the same patronising disrespect as people on this thread.
I don't find that disrespectful. It just shows that not everyone finds broad local/overseas accents easy to understand.
It is your insistence that the accent of some other person that you personally dont have the ability to understand is therefore a "strong accents" or a "difficult accent" which is disrespectful.
DH is from Northumberland. I can assure you that some Northumbrian accent are much broader (stronger) than others. Although, I expect that you would disagree with me. I struggled to understand some of his family when I first met them, but don't at all now because I am used to it.
I live in Yorkshire, and some of the people I work with happily admit that they have broad (strong) Yorkshire accents and are proud of it (and rightly so). This is their own perception of their accents BTW. Then, some of the people I work with have less broad Yorkshire accents.
So, in my experience the two regional accents I am very familiar with (and can understand perfectly well), still come in different degrees of broadness or strength. I defy you to have this "argument" with some of my team mates who are very proud of speaking broad Yorkshire.
When the TV series Coast first hit our TV screens the BBC received loads of complaints about Neil Oliver's Scottish accent because so many viewers couldn't understand him. IMO he was easy to understand, but I don't think the viewers were being disrespectful for struggling to understand or "not trying hard enough".