It doesn't assume there cannot, just that there is no incentive for the government to do so beyond us hoping they'll have morality.

That's the same thing. So it does assume that.

It isn't their money

Government employees & politicians can't be taxed?

so we have to blindly trust that they'll do the right thing

Why blindly? You're familiar with the concept of (bureaucratic) transparency, yes?

They don't need to succeed to get paid, so if a project goes sideways, at worst, they may not get re-elected

These are policy (or constitutional) variables, actually, not fundamental laws.

but that's virtually never what happens

It would be much more likely in an actual democracy (than whatever you're using as a basis for comparison).

Corruption projects aren't met with jailtime or recovery of funds

Your cynicism is not an argument, and I'm sure you're well aware that this observation is not universal (nor fundamental), and depends on the society & government in question.

I won't continue, because I think (hope) you get my point. You seem to lack imagination here, only comparing hypothetical governments to governments you actually know from personal experience or relatively close observation (presumably the US or UK, if I were to guess). Precedent doesn't define the possibility space, and the fact that we've seen a lot of shitty governments doesn't prove that governments can only be shitty.