> They are often competitively priced with air travel

I traveled in sleeper trains in China, and while the experience was interesting, I can't really say it was comfortable or even pleasant. People would keep moving around at night, making noise, and the train would stop now and then and create noise on its own. It's slow and it only works if you are not too far from where you want to go anyway, unless you are ready to waste a long time to get there.