They can't. The days of running 100w tube amps in clubs are over. Everybody I know that uses one is a bedroom guitarist.
Guys I know that are gigging consistently are using modelers or lower wattage amps, for both FOH ease of use and home recording. There just isn't any place that a 100w amp is even feasible for use anymore. How many of us are actually playing stadiums? I know I'm not, and I don't know anyone who does. There are clubs here that won't even let you in the door with one. Sound guys just say no.
For home recording use, modelers and lower wattage amps are just easier to use...I can't even hit 1 on a tube amp here. Cops get called lol.
I know there are guys that will always use them, but guitarists that are coming up now will have grown up using modelers and that's where they're gonna be the most comfortable.