I think they are understaffed. I know for Swift on Windows, there is exactly one person driving that effort last I checked.
The Swift Linux team might have 2-3 people. And knowing Apple, that might not be 100% of their time.
Which cleary shows how much that matters to Apple.
When compared with Oracle, IBM, Microsoft and Google efforts for Linux support for their ecosystems, I really cannot see they work at all, given their output in the last five years.