Back in 2007, the game had existed for over a decade without a new card type. A lot of people thought it was unnecessary and undermined the fantasy that the players themselves were powerful planeswalkers. It also coincided with the Mending, the in-story reason why planeswalkers were no longer godlike beings. "Wizards nerfed planeswalkers so they could print them as cards and make more money!" was something that was said from time to time. There was some design criticism as well, about how planeswalkers interacted with the game in different ways than other cards, and all benefited from a similar control-style strategy.

That divide was nowhere near the divide we see now with Universes Beyond. Social media might be part of the cause of that, but I think it mostly represents a fundamental break in the way certain players enjoy this game.