The basic software like the Intellij Community Edition is also fully open source. (And it's not actually basic at all. It's a great full featured IDE)
Basically you're only paying for their support/updates and for specific language and toolkit support, which makes sense to me. They need to pay their staff somehow.
It's not comparable to Adobe or other crappy manufacturers where you own nothing.
Basically when you buy your subscription you also get perpetual access to the current X.Y.Z version + any future bugfixes (Z). So if you stop paying next year you still have access to the version from when your started your subscription.
If I subscribe for 10 years then can't afford it any more I'm rewarded with a 10 year old version of the software? It should be the version that was current when you finished your subscription.
as soon as you pay for 12 consecutive months, you will receive this perpetual fallback license providing you with access to the exact product version for when your 12 consecutive months subscription started.