I'm guessing the issue is that some malware writers started using nim, and the antivirus vendors then decided to make heuristics that detect nim generated binaries and call it malware.
Also, in Hare's specific case, it doesn't _really_ matter as they will never support Windows or MacOS [1], and there isn't a significant presence of anti-malware software on linux distros.
Mingw might have a higher weight for "this is malware". Then you combine that with nim generating code that's common across most nim binaries (the GC, boilerplate symbols, etc).
Then there's perhaps not enough positive signals to offset that, since there's not yet a wildly popular windows app written in nim.
Probably best to select the top 10 AV companies, to keep the workload down. Per each release, shouldn't be too bad, though likely someone or a group needs to be designated for the task.