You will always have people who buy a jersey every year regardless. You'll have people who will buy all three. People like me who don't buy a jersey every year out of some sense of responsibility, or idea of support, or obsessive compulsion will only buy a jersey if they really like it. So if they bring out a training jersey disguised as a match jersey, or something which looks like the livery of a British police van, then obviously I'm not going to buy it.
But I suppose they know more about market strategy than I do. It doesn't have to be the same kind of design but we all know what works by now for the home kit. You're right that they must feel they need to be different enough to justify charging €60+ for another striped home jersey every season, which most people buy, a smart away kit, and then they go a bit mad with the third. Seems to me that people will buy stuff if it looks good.