My guess is because it becomes a private flight. The aircraft has its cert of airworthness so legally it can fly privately once all the agencies have been paid.
Well you know nothing about private ops and RVSM
Regardless of private or AOC, an aircraft's RVSM approval is cancelled once it comes off the operators ops spec as it is no longer maintained under an approved maintenance program. Same applies to the C of A. If not maintained by a CAMO or on an ops spec, the C of A is invalid.