I often listen for US activators on CW. I often hear chasers and recognise some of the calls of folk posting to this reflector. N4EX for example. But the activators are rarely heard.
The closest I got to an S2S was when trying for an S2S to the KU6J ceremonial activation and I could hear the activation weakly, but my calls could not be heard over the din of US chasers. I heard signal reports like 599 being handed out; if genuine, my much weaker signals had no chance.
After working 20 domestic chasers, many activators vanish and after a minute or so sotawatch says they have moved to 40m or another band where I have no chance. No prop and even more local chasers.
When the US chasers are giving signal reports like 529 I am guessing that the activator isn't radiating much power. This could be due to using very low power, or due to antenna limitations.
S2S contacts outside the US over the Pacific to VK/ZL will only occur if skeds are made on secret frequencies and US chasers are unaware of the activity. Alternatively good discipline exerted by the US activators to insist on local callers standing by for DX could work.
In our mornings just after sunrise I do hear increased signal levels from the US but I don't have a directional antenna. From the call areas heard, I am guessing it is long path to the east coast. West coast signals are rarer at that time of day.
One further result from there being relatively few VK cw operators: there is not so much "local" QRM so DX has a good chance of being heard. I have good ears and can work up to 25wpm when necessary. But I only run 10w into portable antennas so don't expect signals like VK3MO with his triple stack of yagis or quads. It ain't gonna be that loud.
Summary: it isn't just that VK/ZL operators don't use CW (enough). There is more to it than that, especially in these times of very poor propagation.