It's one thing to use a standalone app like MS Money for 20 years with various hacks and compatibility modes to keep it working. Over the time I've used a password manager I've seen OS and browser updates break parts like plugins or syncing. I've transitioned to using passwords more on my phone (and phone APIs have changed).
When you had a computer sitting in your home that connected to the Internet via modem for 2 hours a day, your OS or apps could be riddled with hidden bugs and holes and it didn't matter as much.
Now we are constantly operating in insecure-by-default environments, and (responsible) companies have to spend much more to monitor, improve and maintain their applications over time, as devices change, underlying operating systems change, new threats are detected and published, etc..
Hence subscriptions..