To certify the CDL for missing winglets, the OEM has to flight test the configuration.
To save cash for an option no one want to pay for, typically only 1 winglet removed is tested. If an airline wants 2 removed they can pay for the flight testing to the OEM. Basically it involves revising the performance numbers i,e, measure the increased fuel burn.
PS. I would be surprised static wicks would be an issue in this. The aircraft should have sufficient elsewhere to compensate. I think around up to 1 in 7 may be missing per typical design.