Operating in the general portion of bands generally increases the number of US stations that could call you, since about 1/2 of US hams (not counting technician) have General licenses. But, in contests the band fills up quickly and often the only places left to call CQ are in the Advanced or Extra segments.
Seems like a lot more Advanced/Extra hams are more active in contesting compared to General hams, so that offsets the issue a bit.
73 John K3TN