Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
The subscription model is all about changing their revenue stream. Rather than getting large bumps of cash when a new "version" is released, with 365 they get a steady stream of income that is slowing increasing as more people are forced from the one-time payment model to subscription. A steady stream of income is easier for the bean counters to work with.
Also, over the long run the subscription scam generates more revenue. For example. Say as a 1 computer user/owner I bought Office Home and Student 2003, 2007, 2010, 2013 and 2016 when they came out. That would be 5x $150 = $750. If there had been subscription in the same time span I would have paid $100x13 = $1300 for 365 Home, or $1230 since 365 Personal came out.
That simple assessment assumes that everyone "automatically" buys the new version. The reality is that even now there are still many people using Office 2003 and even earlier, representing "lost" revenue.
One touted "benefit" of 365 is that it allows use on up to 5 machines. Well, that wasn't really relevant until the last few years. Realistically, few homes had more than 3 machines that Home and Student allowed install on. And when 365 came out, MS stacked the deck by changing the H&S license to then only install on one machine. Even so, 365 is only a "better deal" if you have more than 3 machines, a new version of Office is released every 3 years, AND if you always buy the newest version as soon as it comes out ...
Much the same applies to business licenses.
The "free" versions of Office you can get on Android and iphones are dumbed down, short on features. AND, they are free to "encourage" android and iphone users to stay with Office products rather than using tools native to those operating systems. Sooner, rather than later, you can be sure that they will also move to the subscription model.