Discontinuing is fine, the egregious part is not open sourcing it. Huge swathes of internet culture in terms of both story telling, animation and games is locked up in this system they have no interest in.

Either it has value and shouldn't be open sourced in which case why not keep developing it.

If it has no value whats the excuse not open source it as a sign of good will for artists and developers to invest time in your ecosystem, otherwise the message is "If you build with our apps and systems you will be locked out of your work forever when its an inconvenience for us, even if you're paying us hundreds a year"