itch.io

This is likely due to Linux being a second class citizen in most large developers eyes. They want to make one to sell to Linux users, but aren't will or able to put in the man hours to do it to a high enough standard, or maintain it. There are a few good examples of Linux ports running better or the same as their Windows counterparts, games like; Counter-Strike 2, Stardew Valley, Divinity Original Sin, Hollow Knight, Crusader Kings 3, Valheim. Not to mention some fan made community ports such as OpenMW (The Elder Scrolls III: Morrowind port), Arx Libertatis (Arx Fatalis port) and DevilutionX (Diablo port).

EDIT: Add Baldur's Gate 3 to the list of good native ports as of recently.