Why is it, when you install an app from the AppStore that requires an account, and you don't already have an account on the service, you have to fill out a form and create one?

It seems like a dumb question, until you consider that this is not your computer.

I'm trying out Flow, the task-management app, and I must say I'm pretty impressed. The problem is, Flow comes with a 14-day trial, and I'm on day 14. Even though today is only the second time I've logged in and the first time I actually created a task in it. So now I have the dilemma of deciding whether to subscribe based on a few minutes usage. If I hadn't gotten around to logging in today, that would be based on zero usage, and I definitely wouldn't subscribe.