I don't know about the others out there, but I like the freedom that I have to go where I want and when. As an owner op driving for Landstar Express, I can take time off when I want and for how long, we can also refuse loads without penalty.
A couple of comments about straight trucks over t/t, less maintance, easier to get in and out of places. With a ST we don't have to worry about the trailer, we do all live unloads, and "usually" the emergency freight gets loaded or unloaded upon arrival no waiting. Having just 6 wheels we can drive in that left lane instead of being stuck behind slow moving T/Ts, and with the price of fuel, 8 to 10 MPG is better than 4-6 MPG.
We make about a $1.30 loaded mile, we average with deadhead $1.00 per mile, operating expenses are 30%, that's $.70 per mile, and as a team we do about 4,000 miles per week.
Thats some of why I drive a straight truck