If the online ladder isn't your thing because you don't like the tracks you have to play, then maybe try to do good on the MX ladder?
I know we all play for different reasons.
For me, I play for the track building, and just the challenge of trying different maps. I don't try to be the best or have the highest rank in anything. It's just the experience of trying different things that give fun and satisfaction.
Although lately I have tried to improve my rank online a bit, just because it's fun to see how high I can get. I've had so much fun on the "Very Short:)" server which is usually the most populated whenever I get on to do some racing. The maps vary from 10secs to 35secs and there's a nice mix of fullspeed, speed-slide, tech, and even some odd mini and lolmaps. If I don't enjoy a certain map too much, there's usually people on the server to strike up some conversation with so I don't have to hunt it too seriously. Other maps I'll stay totally silent as it's really fun to do as many runs as possible and hunt the best time.
I think the best drivers in TM are the ones who are adept at driving many different styles, from Trial and RPG, to Tech and Fullspeed.... and if you can get good at everything... I think it makes you a more well rounded player and increases your enjoyment of the game immensely. You don't have to say "oh I don't like these maps" or "oh I don't like those maps". It's all about you and what you make of the game and your experience playing them. You can have some fun on just about any map. If the map is too frustrating to hunt a time on, you can always go off and do some freestyle stunts on parts while other people drive it.
That having been said, there's nothing wrong with losing interest either. There's plenty of other things to keep one busy these days. And maybe your interest will be rekindled when we get SM Storm or TM2 Valley next year.
Cya 'round!