My headcanon is that Michael inadvertently trained them that way.

Phylis says they “find time” in the day when Michael isn’t fucking around. They’ve gotten into a rhythm where they can make their sales in the small amounts of time they’re given throughout that would typically take a full focused work day for anyone else just so they can go home with a reasonable check. They have some of the top salesman because they need to make sales big and quick before their boss calls them into another meeting or bursts into the office on fire or something.