The only real argument for leaving Tatum off is he is a front court player which is just deeper than the guards. I don't really have any issue with Giannis, Butler, Embiid, Siakam, Adebayo, Sabonis, and Middleton making the team. That is 7 front court players, you can't put an 8th on the team so if you put Tatum on, you have to take one of those players off. Embiid actually seems like the easiest to remove given his games played, but I expect him to start and I'd have a hard time putting Boston's #2 player (even though I think he is the most valuable, he probably isn't quite as good as Walker yet) in over the #1 player on the Pacers (who are just behind Boston in record), or the #2 players on the two top teams in the conference.
I know Lowe didn't frame it that way, but that seems like a reasonable enough result when you do look at this way. The guards are much weaker and with guys like Irving being hurt, it makes it easier for Brown to get in even though Tatum has been the better player.