The logic of the exclusion
The leaseholder protections regulate what a building owner may recover from leaseholders. They are a cap on one party's ability to charge another. Where the leaseholders are the building owner, there is nobody for the cap to operate against.
The same reasoning excludes commonhold buildings, where each unit holder is a member of the association that owns the structure and common parts. In both cases the conclusion follows from the design of the scheme rather than from a judgement that these leaseholders need less help.