I remember emailing the Maine Turnpike Authority in 2020 about why variable regulatory speed limits are limited to ORT plazas and got the following response at the time:

We do not have any plans at this time install variable speed limits signs at locations besides the ORT plazas. Our flashing 45 MPH signs are technically advisory signs, however motorists can still be issued a ticket for imprudent speed. ORT plazas are different than the rest of interstate and making it regulatory vs advisory prudent.