Well they didn't want New Vegas to compete with Skyrim. The last thing they wanted was for Obsidian to steal their thunder and have New Vegas out sell Skyrim. Damn shame as New Vegas blows Skyrim out of the water with its RPG mechanics and story.
It is interesting noticing how different the campaign for
New Vegas and
Skyrim were. I can't even remember
New Vegas's trailer, but everyone has seen, and remembers,
Skyrim's trailer. Maybe there was a hint of deliberate sabotage on Bethesda's part there, but I dunno. It's a motive, but is there proof? That motive can be countered with, "wouldn't Bethesda want every game it publishes to do well, at least financially?"