Why on earth would you "have" to change it?
Repainting isn't obligatory!
I've got a room that's the same colour as when I moved in 8 years ago - I like the colour and it's in good condition, why would I waste time and effort repainting it for no reason?
Even for people that do want to change every room most people dont do it "when they move in" - they save up money, work out what the light is like etc and then do room by room....and it's a lot easier to live with plain colours in the meantime than with a witch staring at you from the fireplace!
In that house its not even as though you'd just have to replace the walls - the ceilings would need doing in some of the rooms and that's a much harder job. Not to mention at least one fireplace etc. It is in no way comparable in time, effort and cost to giving a magnolia/white wall two quick coats of blue.