The reason that so many bags have to be gate checked is that the Gate Agents aren't enforcing the number of carry-on's and the flights are almost, always full. Passengers aren't considering their fellow passengers when they bring 3 carryon's, with them and rush to get to the cabin, first to get the available bin space . The available underseat and overhead bin space, haven't changed.
Not sure what airline you're talking about charging $25 to checkin luggage, as Air Canada allows 1 free bag, can't say that about the US carriers.