Probably LMIA is not really and option for low skill jobs like retail because it isn't worth doing it. For high skill it is probably worth it.They can easily hire foreigners without offering guarantee PR. If they streamline LMIA for those on demand jobs, you will see several applying for TR without even thinking if they can remain there permanently. Some don’t even want to. In the US, several Mexicans just want to work and send money back, because the exchange rate makes what they earn so valuable.
Just guessing here.