There are several great reasons to take high speed rail over air travel.
-No hassle check in. You just get a ticket and get on the train.
-Train stations are usually in city centers rather than on the outskirts.
-Easier to implement value added services, such as dining cars, vending machines, internet access (cell phones work too), and I've even been in a train car that was an improvised movie theatre. After the train started moving they turned off the lights, pulled down projection screens in the aisle, and played the movie with surround sound etc. Good way to travel if you forgot your book
Another interesting feature is low cost freight. Say you have something heavy or bulky you want to ship across the country. Rather than paying exorbitant shipping rates, you just get it to the train station, they put it on the freight car and the receiver picks it up same day from another station down the line. A third party could even coordinate the whole thing (the delivering and receiving) which would should save you money as well.