As a rando racer (and a racer in the Brundage race that Jonathan attended) I feel compelled to answer.
I totally understand not "getting" resort-based skimo- it is definitely an acquired taste. Especially skinning at resorts, when you can literally ski 5x as many laps if you just take the damn lift. The simplest cop-out answer that might satisfy you is that here on the east coast we have no choice! If you're scheduling in advance only resorts offer reliable snow for any kind of ski races, particularly those that require long uphill skintracks with downhill sections that can be linked up, there really aren't any reliable backcountry options.
But assuming that answer isn't satisfactory and the question is more generally "why skimo," I can say that I got into it because a) I love to ski, b) I love to be outside skinning, c) I enjoy moving fast and efficiently, and d) I enjoy pushing myself and improving physically- skimo is a way to do all of those things, with like-minded people, in at atmosphere of *friendly* competition. It's not unlike the trail running scene- full of friendly athletes who will share a beer with you after and tell you all they know about the sport to help you improve. Good people that will cheer you on even if they pass you. And coming from nationals last week, I can tell you this is true at the national level as well- if not more so.
Also, FWIW, I think skimo racing is one of the hardest and most complete sports out there. To be competitive, you have to a) be fit for the uphills, b) be strong enough to ski confidently down immediately after pushing yourself on the ups, c) be an excellent technical skier, on skinny skis where you can't rely on the ski to do all the work, and d) master the art of skimo racing- e.g., gear management, transitions, etc. Being good at all of these things makes you a better backcountry skier, without question. Also, pulling it off in a race, where everything aligns and you ski 5000+ vert in a matter of 1.5-2 hours after pushing yourself to the limits- the whole experience is tremendously gratifying.
Now clearly this isn't for everyone. You have to be pre-disposed to like endurance sports, which requires and appetite for a bit of suffering. And if you want to improve (also very gratifying, just like getting better at guitar or woodworking, for example), you have to be diligent and set long-term goals and make plans and stick to them, which yes means structured training, which also can mean making sacrifices taken to the extreme. Some people dig that, others prefer the flexibility to just ski whenever you want and whatever you're in the mood for. IMO Both approaches are valid- but that's why this is such a great sport, it's different things to different people. I love powder skiing as much as the next guy, but I am wired to enjoy pushing myself. It's not about being the best or beating everyone else - but really is about seeing what I can do and how efficient I can be.
Regarding being/feeling "free" in the mountains, FWIW I personally feel the most free when I can travel great distances while thinking as little as possible about my gear and equipment, transitions, etc, and keeping it as simple as possible- all of which is part of the skimo experience.