Every Mac transitions to ARM, only a very small amount of Windows PCs are running ARM. SO right now there's not an large user base to incentivise software to be written for it.

You are right that Windows on ARM cannot be called a success. But if you make Windows/macOS cross platform software then your software needs to be written for ARM anyway.

So if you support macOS/x86, macos/ARM, and Windows/x86, then the additional work to add Windows/ARM is rather small, unless you do low-level stuff (I remember Fortnite WoA port taking almost a year from announcement to release due to anticheat).