It's quite simple. The only people pissed off at his new rule are:
1. Pirates who will never ever sub to any dev since now they can't play for free.
2. Those who will only join for a month from time to time.
Those who support multiple devs for more than one month are the folks who give developers the majority of their income, they don't care if they have to sub for two or more months since they intend to stay anyway.
Also it's funny when I see people saying "why wait a month after you already purchased the game" You all seem to forget that this is Patreon and not Steam. You don't buy the game, you subscribe to the dev, so more or less he can set this up however he wants for as long as it's announced, so people know before subscribing.