It's not so much that the Founders didn't grasp partisanship as it was that they thought it incompatible with republican government. Their conception of "good government" was a society governed by an aristocratic class of landed gentry, whose wealth would (in theory) make them immune to temptations like bribery and self-dealing. Ordinary people couldn't be trusted with their own government, because they would too easily succumb to those same temptations.

In practice, of course, that theory broke down almost immediately. Political parties started coalescing around Hamilton and Jefferson practically before the ink on the Constitution had dried, and the gentry whose disinterestedness the Founders had placed so much trust in turned out to be just as flawed and venal as everybody else.

If you're interested in why the Founders thought the way they did and the process of how reality broke their worldview in half, I can't recommend Gordon Wood's book The Radicalism of the American Revolution (https://www.goodreads.com/book/show/6956.The_Radicalism_of_t...) highly enough. It's a great read that will change the way you look at the Revolution and the early republic.