Seeley and Tomac are not Teammates they just ride the same brand of bike. Seeley is on the Troy Lee Designs Honda squad, while Tomac is on the Geico Powersports Honda Squad.
And like any other sport, you have your buddies that you grew up with, ride with, share rooms or rides to the track with........ etc. I don't know the personal history of Seeley and Tickle, but I wouldn't be surprised if they were friends as they are the same age, ridden the same tracks at the same times for other teams, and are top prospects.......... Nothing wrong with wanting your buddy to win if you can't do it yourself.
And when you're racing, everyone you are out there with is on the "other" team as it's everyman for himself except at the Motocross Des Nations team race.