There are probably several reasons. Firstly, I think my set came out in 2011 (it might be a later repackage as the original used full-size cases and mine uses the slimmer ones), so the distribution companies likely only have a certain number of years in their contract. When the new company takes over, they realise they can reduce their costs by compressing the video and squeezing more episodes onto fewer discs (mine has three episodes per disc like my Dukes set). Secondly, the US and Europe use different TV systems (NTSC and PAL), so the TV shows have to be converted when they cross the Atlantic.