The problem is there's been a ton of work on chained garbage collectors, and the frustrating and seemingly non-intuitive result that everyone eventually hits is

The problem is there's been a ton of work on chained garbage collectors, and the frustrating and seemingly non-intuitive result that everyone eventually hits is that you have to collapse down to a single garbage collector to get garbage collection to work reliable. There are just too many edge cases when you have, say, a native browser garbage collector and a separate application garbage collector, with references held between them. That's why mainstream support for C# -> WebAssembly is on hold until WebAssembly exposes native garbage collection support.