You know full well that if they put a Welsh language sitcom in that wasn't particularly good (yes I do remember it) then it would be tokenism.
It's like doing a list of the top 20 UK footballers and there's no Northern Irish or Scottish players in it. It doesn't make it English/Welsh only. It's reflecting reality, or in this case popularity.
A best loved list can't include programmes that 1% of people have watched. That's just the way it is.