That is not entirely accurate. If you take the ECL and even the first edition of BOA the 1v1 ratings were used as a much higher weight than the team game ratings. Considering the state of DE TG rating, not using at all makes sense to me.Voobly tg ladder was used for seeding as well.
I love the RoR guys for instance, but if they played any of the top 3 teams they wouldn't win a single game, let's be realistic.
Only a handful of teams actively play on the TG ladder when most players have a fairly accurate 1v1 rank as well, which to me also indicates it is a fairer evaluation of skills.