why does it take long for Rescue me to come out on dvd in the uk?

The 3rd series came out last year.and am aware that there are seven
seasons, but the UK is like four years behind it will be like late
into this decade before all the seasons come out.....any ideas why?
ive checked the internet for dates when they come out.from series 4
onwards they have yet to be confirmed..even Region 4 has a release
date coming.