Also, why aren't they willing to just restrict Workshop?
Driving to Oregon for work last week, I was listening to the So Many Insane Plays podcast that came out recently, but before this announcement. Kevin Cron and Stephen Menendian made a pretty reasonable case that nothing needed to be restricted in Vintage given the current metagame. Workshop decks had been doing well, but there's a statistical fluctuation in Workshop performance in Vintage, a kind of ebb and flow as they do well while preying on vulnerable decks, then do poorly as more players sideboard against them or play decks that aren't so soft against artifact-based control. At least some of the perception that Workshop decks were now over the top, moreso than normal, could be blamed on the VSL, which is more high-profile than Vintage at large, but has a small sample size and a different distribution of decks than Vintage at large.
I'm uneasy about the prospect of weakening Workshop decks too much, as it would upset the balance of the format. Before the restriction of CotV and the rise of Dark Petition, people were seriously underrating ritual-fueled combo decks just because they were either easy prey for Workshop decks or dedicated too much to shoring up the matchup and weakened themselves against the rest of the field. At some point, if Workshop decks can't counterbalance ritual-based storm combo, then Storm would become the bogeyman of the format, presumably requiring the restriction of some component...
