If they have no incentive to upgrade, that's because the newer versions don't add any value for the user. This makes sense: 1Password is a pretty mature product at this point and there probably isn't much room to add new features, unless you want to expand the scope of the product.

That is to say that I personally (and again, this is just my opinion) don't care about any new features and would be unlikely to upgrade from version 6 on that basis. I may upgrade to ensure I will continue receiving security updates and OS and browser extension compatibility updates, but it would be nice to know how long such updates to version 7 are guaranteed for (presumably they will eventually release version 8 for a new fee and discontinue such updates to version 7).

> (and servers / APIs for it)

The users (like me) who are against subscriptions are only using local vaults (managing the storage sync ourselves) and do not care for or want the web/sync services.