some affiliates do because they have local news on Saturdays
As an example WCCO (CBS Minneapolis O&O) has E/I from 9-11am on Saturdays and 7-8am on Sundays (they have local news from 8-9 on Saturdays)
And WBTV delays CBS This Morning: Saturday to 8-10am for local news from 7-8 am which bumps the third E/I hour to 7-8 am on Sundays. If not for the E/I rule I am sure they would air local news on Sunday from 7-8 am too.