This does seem to be a popular concern amongst so many members here considering three quarters of the similar topic threads are laments about the modesty of other guys when they are changing, showering or taking a piss.
As I've added many times before, I don't concern myself with what others are doing in the gym locker room/bathroom nor do I have a need to remove any article of clothing myself 99.99% of the time during my visits, let alone get completely naked. I am there to workout, get it done in as little time as possible and go on with my day. My home is the place to shit, shower and shave...not the gym and just from casual observation, it seems like most of the other clientele are the same. Every gym locker room I've ever seen has had separate shower stalls with a smaller curtained area connected to the shower proper that the guys that do use the shower utilize to get undressed or dressed and not the common locker area. This seems to be the standard nowadays, at least for big-box gyms.
As far as your opinion on the practice of not showering at the gym after using it being gross, it is just that...your opinion. Besides the fact of not being a big sweater, I don't go to the gym to do balls-to-the-walls, hours long cardio or powerlifting routines and am no less fresh leaving the gym then when I came in and am usually going right home at any rate. So, while there may be a reason for guys to routinely shower at the gym if they are doing P90X and CrossFit, end up a soggy mess and have to go to work or a social function right afterwards, I see little priority to waste another 30 minutes to use a gym shower and risk all kinds of diseases in the process.
The bigger question that must be asked, once again, is why does the fact that the majority of men are not willing to walk around naked in front of you, bother both you and so many others here? The majority of dudes are using the gym to improve themselves, not to serve as eye candy for those hoping to catch a glimpse of real-life peen. There's a ton of naked pics out there, including locker room ones, both staged and maybe not so staged. Which also brings up the answer why many men aren't willing to strip down in front of others, especially given so many others can't be without a phone in their hand for a second, even in the locker room and thus there's always the possibility someone's semi-private nudity becomes very public.