Rocket League also dropped Mac support, which would be perfectly compatible with the store, so you can’t argue it was about Linux. The actual reason was the need to upgrade to DX11.
Payday 2 has no connection to Epic, but it’s common for developers to revisit and update games when releasing on a new platform. For example, the upcoming Steam port of THPS 1+2 even has a new developer behind it, and set to include achievements and potentially other perks.
There are also games like Rust that have dropped native Linux support without any ties to Epic.