🙄 Stop yourself. These are poorly informed assumptions in 2022.
As a developer who has worked with Mono on Linux on multiple occasions, I find it difficult to buy this excuse in 2022 because:
* In Affinity's case, Mono is particularly well supported on Linux, but we even have straight up .NET now. This has been the case for some time now. (Unity 3D, OpenRA, etc.) The Mac version probably already uses the same backend. 🙄
* For distribution, AppImage format works, is used by both Krita and Inkscape highly successfully.
I'm more inclined to believe there just aren't any Linux-inclined developers on staff, or resources are tight enough that its difficult for Affinity executive(s) to justify the Linux build. Once the initial legwork is done, continually pushing out a Linux build would be simple.
The very least Affinity can do is what they are doing now, attempting to guide people who are having this work in Bottles on Linux.