For short trips. Most plane trips are at a distance where there isn't a viable alternative. Sure there are some nice trains that can handle the more common trips, but airplanes really shine for much longer trips.

And planes go to more places than trains do. You want to add a new destination? Go through a few years of planning and construction for a couple thousand feet of tarmac, and people can go there using existing planes. Best of all, you don't need a large passenger base to justify the expense.

For rail? You're looking at an order of magnitude more for planning and construction, all new infrastructure, all new rail stock. It will take a much larger passenger base to justify the expense and effort.

Airplanes don't just shine for longer trips. There have been some interesting developments with commuter airplanes that are either all electric or hybrid with a 200-plus-mile range. If they are as energy efficient as they promise to be, we could see a resurgence in municipal airports for transportation between regional centers where rail is either unavailable or excessively expensive.