Do you see any pricing on the community version page?
Why would you be able to download a piece of software for free and then be locked in with updates?
If you don’t want or can’t pay for Zammad support, then that is absolutely fine. We as vendor pay our bills via custom developments, feature sponsorings and our support customers.
What is not free is the time you take to install and maintain Zammad, nor the server you have to run / rent to do so.