Subscriptions bleed money from users continually, regardless of how often they use something. Paying for major upgrades only allows the user to upgrade based on whether they need certain features and potentially skip every other update or so if they use the software only lightly.

For example, my personal at-home copy of MS Office is the 2003 version. I use it so rarely that this does not matter, especially with other options available that can view and edit MS Office documents.

I stopped using VMWare Fusion, for example, because they got into the habit of releasing paid upgrade versions that were required in order to run on Apple's new OS X version. Perhaps it's not their fault that Apple's OS updates broke VMWare's virutalization, but I don't use this often enough at home to want to pay for an upgrade every year. Before I would pay for an upgrade every 2 or 3 years. Now I've switched to VirtualBox at home.

For business use, software is used much more often and it matters a lot more to have it up-to-date. So in that case a yearly subscription might make sense.