In other, more productive ways, I assume. BTW, as they currently do, in addition to the kneeling/sitting during the national anthem.
In the weeks after the initial Kaepernick incident, I paid some attention to what was going on. Rex stood, but did NOT put his hand over his heart. Most fans stood, but kept their hats on---many just chatted away. In years past, sitting wasn't a big deal during the national anthem, until it became one, last year.
I think it's become, for most people, one of those rote traditions, people just do, without thinking. Like the pledge of allegiance before school (did you really think about what you were saying?) and most of that goes on in Catholic churches (and I assume, most other organized religions).
IMO it is a disservice to the national anthem to be turned into something that is "just done" and not truly felt from the heart. I think keeping it actually "special" would make it more effective.