Tack on having to pay Apple to play in their shitty ecosystem and it makes complete sense.
Wine/proton as a gaming ABI/runtime is perfectly fine, Microsoft used to do a lot to maintain backcompat and that spirit has clearly distilled into proton: it even runs games Windows is unable to (most recent example of mine is Black and White).
They probably stopped supporting macOS when Apple introduced the notarization bullshit. Can't blame the DF team tbh, macOS is a royal PITA to support (even without notarization), Apple doesn't mind breaking stuff from one OS release to another.
If I were making games I wouldn't support it either. Apple does just about everything to not support backwards compat.