Well, and they're often slower since they require mutating the reference count on every single time a field is stored. You can optimize that using lazy reference counting, or not updating refcounts for references on the stack and instead scanning the stack before a collection. But at that point... you're halfway to implementing a tracing collector.

Every refcounting implementation eventually gets "optimized" to the point that it has most of a tracing collector hiding inside of it. I think it's simpler, cleaner, and faster to just start with tracing in the first place.

There's a reason almost no widely used language implementation relies on ref-counting. CPython is the only real exception and they would switch to tracing if they could. They can't because they exposed deterministic finalization to the user which means now their GC strategy is a language "feature" that they're stuck with.

That being said, ref-counting is fine for other kinds of resource management where resources are pretty coarse-grained and don't have cyclic references. For example, I think Delphi uses ref-counting to manage strings, which makes a lot of sense. Many games use ref-counting for tracking resources loaded from disc, and that also works well. In both of those cases, there's nothing to trace through, and the overhead of updating refcounts is fairly low.