CTRA Race 1 is always populated. I don't know about the UK/European times, but you are US as I am and CTRA is always at the top.
The fact is, there just isn't that many racers in the US. Even with S2, you can count the number of populated servers on one hand.
There are probably 4 times as many demo servers populated during US times as there are S2 servers.
You have taken a small step for getting more racers in the US, you purchased an S1 license. Race the CTRA server, tell as many of your friends who are race minded (rather than driving game minded) about LFS and get them into LFS. If you move up to and S2 license in the future, you get 4 of your buddies to join, and each of them get 2 buddies each to join LFS, you'll probably increase the US LFS userbase by 10%!
Racing just isn't as big in the US as it is across the Atlantic is what I'm figuring. We're too busy trying not to lose our homes to worry about motorsports.