What are the purposes for which Red Hat finds the spec license tags
useful?
I am still interested in this 

History reason. I guess.

I recall that 15 years ago, few maintainers I spoke with were proud of design of spec files that everything is in one file in declarative way (hence the tags). This was opposed to debian way - one debian/ directory with bunch of files.

This dogma was already broken with `changelog` files and specparts.

Therefore I would hesitate to say that RH is not willing to change anything.

-- 
Miroslav Suchy, RHCA
Red Hat, Manager, Packit and CPT, #brno, #fedora-buildsys