Pot calling Kettle
I don't know how this is different from any hardware/software platforms. Sony, Microsoft, Nitendo, Apple, Disney, etc. all participate in this lock-in.
You can't purchase a game for one platform and hope to run it on another platform. If I bought a Windows game, I can't ask to get a corresponding Mac game for free (unless the publisher gracefully gives a free license). You have to re-purchase every software to move from Windows to Mac, or from Android to iOS.
This is not just software, but also any digital media. If I bought a DVD movie, I cannot ask to get a free BluRay media or streaming of the same movie in the same resolution (unless you explicitly paid for several formats in a bundle) without re-purchasing the new formats. If I bought a CD audio, I can't ask to get a free DSD or 192k audio, or even the same resolution FLAC format over the Internet without re-paying. Just the act of downloading is illegal, even if it is exactly the same as backing up your CD you already own.
I think Epic is just being greedy. They should just focus on increasing Linux games, then complain about lock-in after that.