I think it's spite on the part of the people who make them.
Seriously though, I think the government could do everybody a service by coordinating so we don't have to download a new app in every single town we try and park in.
I've got an app that lets me use my phone as a borescope.
And another one that does car diagnostics.
But my best app, gives me all the cricket scores.
I'm not going to bother counting them, but I'd guess about half the apps that I have actively downloaded myself, are for paying for car parks.