Short answer: we do, just implicitly.
A possibly more enlightening way of looking at things is the following.
In Ordinary Least Squares, we can consider that we do not model the errors or noise as $N(0,\sigma^2)$ distributed, but we model the observations as $N(x\beta,\sigma^2)$ distributed.
(Of course, this is precisely the same thing, just looking at it in two different ways.)
Now the analogous statement for logistic regression becomes clear: here, we model the observations as Bernoulli distributed with parameter $p(x)=\frac{1}{1+e^{-x\beta}}$.
We can flip this last way of thinking around if we want: we can indeed say that we are modeling the errors in logistic regression. Namely, we are modeling them as "the difference between a Bernoulli distributed variable with parameter $p(x)$ and $p(x)$ itself".
This is just very unwieldy, and this distribution does not have a name, plus the error here depends on our independent variables $x$ (in contrast to the homoskedasticity assumption in OLS, where the error is independent of $x$), so this way of looking at things is just not used as often.