I agree, it is not that there is anything wrong with it on a crop camera (though I'm sure there are some FF users that will disagree with that statement), it is just that now there are now better options for crop cameras. These options include F/2.8, IS, and longer focal range.
The constant f/2.8 are better in aperture, range, and IQ plus most have IS.
Except for the constant f/2.8 versions all IS with better range lenses are variable aperture with all the high ends being f.5.6 (most low end f/3.5) with many(most?) users ranking them below the L in IQ and build (the Canon 15-85 and Sigma 17-70 f/2.8-4 being an exceptions for IQ). And all are arguably poorer in aperture. So IMO the only benefit of these over the 17-40 are possibly price, IS, and range.
So unless you also need the lens for a FF and or a film camera the constant f/2.8s are typically considered a better lens on a crop cameras.
Nice pics by the way!
Now the OP says she (assumption photographer is a woman since a guy is in the photo with the baby) got a heck of a deal, then maybe the decision was made because of the price on a (IMO) excellent lens.
I too picked up my 17-40L because of a fantastic price. I will pick up a FF (beyond my film cameras) at some point and that was the first lens on buy/get list when that happened. A used one for an excellent price came up, and I could not pass up the deal. It is excellent on my crop camera.