In most cases it just boils down to the issue of how much you have invested in a given platform.
Yes, there's that emotional attachment thing going on for brand loyalists, but in most cases it's a much simpler issue of how many games you have for a given platform, how much content you've purchased for it, how many hours worth of game saves you have and maybe even how many trophies/achievements you've accumulated.
Because let's be serious here; if you have say, over 20 games, over $100 in peripherals/controllers, over $200 worth of DLC, whether that's games, DLC, whatever, or hundreds of hours worth of game saves, you're not going to just sell your console and all your games and peripherals for a couple hundred bucks and start over on a comparable platform. That's just a stupid waste of time and money.
If you've been on a platform for less than or about a year, you haven't accumulated more than a handful of games or bought much DD content, then sure; it's a lot easier to transfer platforms and start over.
