It's completely possible that it's not! You could be doing useless moves or working out too long, causing the breakdown of muscles instead of building them.
Today, as I was training a client, we were both pretty distracted by a young male doing some weird cable climbing and pulling that in no creative way inside our imaginations, could benefit him. I had to speak up to give him some pointers or a little guidance because that's my nature. The nature of what I do is to guide and help people in the fitness realm. He got quite defensive which I knew was a risk but I let it be and told him he could incorporate what I told him into his current routine to get some better results. Maybe this was not the reason, but a lot of men don't like taking advice from women when it comes to strength and fitness. Not all, just some. Truth be told, I could have definitely whooped his ass in a pushup competition...but not the point. Men and women alike, we all want results, that's why we try. Let your guard, ego and ignorance down, know that not a single trainer out there knows it all so you damn sure don't.
In the meantime, be open and receptive to learning new techniques, read and listen to fitness and health advice. It'll help you! Some things to consider:
You need to address your weaknesses. If you're working out consistently, then great, you're already on the way however, if you don't attempt to strengthen your weak sides, muscles, imbalances, then you will only further worsen them, creating a stronger weakness. You need to catch up the weaker issues to the stronger, so that the body can function as a better whole.
Incorporate compound movements to recruit the whole body, as our movements as humans are not generally isolated. When you bend down to get something or go to open a door or walk up stairs, you're not moving just one joint or muscles group, you're recruiting everything.
You are working out way too long in the gym. 3 Hours is not needed. As a matter of fact, the more intense your workouts are, the shorter the time you should be in the gym. You will tire out quick if you're really going hard. I do cardio but I love to do interval training, even more so outside. Outdoor workouts challenge you in a different way. However, if you're like me and hate running in a snow storm or rainstorm, then you are kind of forced to workout inside. I will do treadmill or stair master HIIT, going intense with speed and inclines for short periods of time and recovering for a minute to lower the heart rate. This is a sure fire way to hit the fat burning zone. There is NO need to do one hour on the stair master. It takes up more time, you want to just fall off of it and it can dip into any muscle that you have already built.