Basically lack of polish. Nim's compiler just keeps evolving around unfinished and unpolished ideas never reaching a momentum.

It's a research project of its BDFL and he is alienating the most senior developers and contributors to Nim's ecosystems (ie Zedeus).

And yet I dont see any Flutter macos apps at all.

Nim could do better with more than just 1 or 2 brilliant developers

For small apps I use exclusively SwiftUI for anything more complicated I use a combo of Sciter and Swift (courtesy of https://news.ycombinator.com/user?id=c-smile).

There are still a lot of rough edges when it comes to look and feel on Apple platforms but it gives me the performance and speed while also being multiplatform.