I think it's fairly obvious why they want people to refer to them as a brand—they don't want to lose their trademark. If LEGO becomes so generic as to lose its

I think it's fairly obvious why they want people to refer to them as a brand—they don't want to lose their trademark. If LEGO becomes so generic as to lose its association with the company that created it, then they lose out to all of the copycat companies. Velcro has done the same ("hook and loop, one side's a hook, the other's a loop"...).