Just because really... I have always hated what they did. Although to be honest there are plenty of things to hate about modern football.
What is the most hated and despised team in English football and why?
While there are always inter-club rivalries, for most neutrals the club they hate apart from their local rivals will probably be Milton Keynes Dons, AKA “Franchise FC”.
Its about 20 years since the new owners of the then Wimbledon club somehow persuaded the FA to allow them to move the team to another part of the country, in defiance of the spirit (if not the letter) of the FA’s rules, thus by-passing any need for this new club (which is what in effect it was) to fight its way through the non-leagues like every other club has had to. In the process the move put out of business a non-league with nearly 100 years of history.
The new owners then changed the name of the team, having told the FA they would not do so, while the FA tried to stop Wimbledon fans from setting up their own team - AFC Wimbledon.
AFC Wimbledon was formed, and worked its way through the leagues in exactly the way that Milton Keynes said was not possible, to the point when they were for a period higher ranked than Milton Keynes. When the two teams eventually met in a league game Wimbledon refused to publish the name of Milton Keynes anywhere in the programme for the match.