It's not the first time that a streamer scammed their subs and friends, hell, there are tons of cases that got more than 10x the attention that the Silker's case got and Twitch didn't do anything

Most likely this change in the TOS and policy was caused by the backlash twitch got from the public after the twitch employees/staff were caught receiving "bribes" from gambling streamers. That could've snowballed out of control for the company and it would've been a really nasty situation for them so they acted quickly and made the appropiate changes. Props to them for that