FTDK, I don't think it's so much that being IFR is busier than VFR, rather that being two pilot into a busy CTAF at 250 knots can be busier than being single pilot into the same CTAF at 180 knots. I think it stems from a couple of things. One, the procedural way the crew work make it more difficult to put things on hold while radio calls are dealt with. Two, there can be a lot more chatter involved between the pilots when establishing their situational awareness. When I'm single pilot I can very quickly disregard or listen to radio calls as I see fit and I get my situational awareness from what I hear, I can also easily massage my cockpit approach sequence to fit into what's happening around me, I don't need to explain to someone else what I am doing and keep them in the loop, and I don't need to discuss things with them in case their situational picture differs from mine. Of course there are many benefits of multi-crew operations, e.g., if my situational picture is wrong and I'm single pilot I don't have someone else to put it right, but multi-crew can get a bit cumbersome in busy CTAF radio environments.