You need some kind of cue to keep in step. If you can see the other guys feet, that helps, but often tinted you can't. The sound of yourself matching helps, but without some occasional cadence, or other governing factor, the speed of the match tends to change in a collective sort of way. My BMT platoon would get faster as we marched, unless the DI shouted at us occasionally.

It's certainly possible and even likely that there were people marching who just didn't give a fuck or were purposefully marching like shit, but as somebody who's served and marched plenty, you'd be surprised how quickly things get messy. It's easy, sure, but it can get out of hand quickly.

If one person goes out of step, especially with no cadence cues, those behind follow the one who's fucking up either consciously or subconsciously. Then the one who's leading the out of step march shuffles to get back in sync, forcing everybody behind them to have scramble to shuffle back into step. It's a domino effect.

Like I said, I won't say it's not possible that you're right, but if you were to watch any marching group you'd see people out of step in almost every case. Regardless of if they wanted to sabotage Trump's parade in this case, most of the people I served with wouldn't want to intentionally make their unit look like a bag of hammers - which sloppy marching does.

I think a lot of people are over analyzing this but like I said, it's still possible that what you believe is true.