The demanding thing with cycling (or endurance sports) isn't the amount of hours you do per week. It's two things really that kind of separate it from other sports: 1) Consistency. If you miss an extra day or two each week, that will show up in races. The biggest way to gain fitness is just to be consistent. And to be consistent with that many hours a week, means you have to make sacrifices. And those sacrifices make it seem like we take it very seriously, because to us, those sacrifices are worth the price to be "good" at bike racing. 2) Off the bike. Our training doesn't end when we are off the bike. We can't take the time we spent on training or racing from sleeping. Matter of fact, we have to sleep more than the average person, to recover. We also have to eat like crazy. If you skip a meal, or eat improperly, at some point, you'll feel that on the bike. There's even more sacrifices you have to make here, which again, makes it seem like things are very serious.
I personally took cycling way too serious. Realized it wasn't getting me anything. And I decided those sacrifices I were making were not longer worth it. So I just ride when I feel like it now. But I know I can't race, even for fun. Because I'll suck. And if I suck, I'll want to do better. And if I want to do better, I'll take everything serious again. It's an endless cycle (pun intended).