When you do something that is important to you, do you try to do the best you can, try to make it perfect? (Perhaps with the realization that it cannot be perfect.) Or do you think, "Eh, imperfect is good enough?"

"We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence,[note 1] promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America."

More perfect implies imperfection, just less of it.

You hit where you aim.

At long enough distance you might even want to aim higher than the target.

more perfect does not imply 'perfect' is the goal nor should it be.

"More perfect" in this context is effectively "better."

Perfectionism, ironically, stunts improvements.

To other answers here: the phrase in the poem "we're not trying to be perfect" seems contradicting the goal "to form a more perfect Union", unless you think that "let's be perfect" and "less be more perfect" are different enough. I think the road to perfection shares parts with the road to more perfection - often.

I think that it is intentional to underscore that "more perfect" != "perfect". The founders that wrote that document did not believe the Constitution was perfect, they knew it a part of process towards perfect, while it might imply perfect is an end goal it also doesn't necessarily say that.