> Aren't there provisions in the standards that allow for spectrum sharing with unlicensed bands?

There are, yes. But there is typically a bit more to it than just writing out a cheque to the regulator.

There's an application process involved, no guarantees of approval, and ongoing compliance requirements (with the ultimate possibility of revocation of license, of course).

For example, if you're within a few KM of certain military sites (typically listening stations) you'll get an automatic rejection.

e.g. From in UK:

https://www.ofcom.org.uk/manage-your-licence/radiocommunicat...

(expand the drop downs at the bottom to see "Shared access guidance", "Frequency Assignment Criteria" and "Interface Requirements")