It's most likely that the three different platforms mentioned were developed and evangelized by three different teams at Samsung that never talked to each other. Each team probably thinks their solution is *the* solution.
It's much simpler, actually.
1. Samsung released Gear, based on Android. Major complain: miserable battery life.
2. Samsung released Gear 2, based on Tizen to address the major complains, battery life among them.
3. Google warms up to wearables while at the same time upset about Samsung diverging (and not only on werables). They approach Samsung and pressure them to go back to the official Android way of doing things. Thus, potentially, next Gear might be based on the Android again.
When I worked at Samsung, divisions were heavily siloed, and often the first time you heard about what they were doing was when you saw it on a news site. Even within the same platform, teams were heavily divided. Our software dev outreach teams didn't even have a way to talk to the hardware design teams.
Haven't worked for Samsung myself. From what I heard, your experience reflects most of the Samsung. But the Galaxy phones were so successful, that they treat them very differently. From the scarce accounts, as far as I can tell, the whole Galaxy development is vertically integrated to allow them quicker response to the competitive threats. (The problem, I heard, is that Samsung bosses, seeing Galaxy development being very successful, now throw all possible carp onto it, hoping that the business unit would also fix other broken products too.)