If they sold a large number of motherboards to end-users and resellers who didn't have need of them, then it's only logical to assume that a good portion of those boards ended up on the reseller market, and may now be competing with sales of additional boards.
Intel's upcoming CPUs should be compatible with those existing boards, at least after a BIOS update, and AMD's new lineup probably won't be coming until sometime in the last quarter, and might be limited to the higher-end initially, so sales of boards for those processors may be rather limited this year.