Re: It's not gravity - it's bulimia.
It's not that simple - you can force customers into a subscription without collecting data (i.e. Adobe Lightroom before they made the "full cloud" version"), you can collect data without a subscription (i.e. Android or Windows 10).
The subscription model is not new - it was how software was "sold", or better "rented", for most Unix workstations in the '70s-'80s. It does ensure a steady cash flow, instead of attempting to sell upgrades. Bad for customer who use it occasionally, good for the company balance sheet.
Data hoarding is a different matter, although it does often come along with the subscription model (they may not want to pay for all the data storage). If and how it generates money really is still to demonstrate. Sure, some like Google and FB made them selling the idea of "target advertising" or the like - some others believed it, but if it really works is yet to see. I believe that if it really worked, we would see on web pages a few well placed ads, and not the mess we actually get.
I'm quite sure they're selling data "invisible to anyone who was unfit for his office, or who was unusually stupid". Of course, spamming billion of ads will generate some data useful to say "See? People actually buy from ads!".