Anyone else a little bit surprised at how the tide has turned?
Not in the least.
From day one Koeman has been very careful to keep his distance from the club, he emphasised at every opportunity how he doesn't have any kind of emotional connection with Everton apart from the contractually obligatory stuff, how he's merely doing a job. Which is fine, I've got no problems with that, but it's what could've bought him time and goodwill with the fans (like it did for Martinez).
He chose not to buy that "get out of jail free" card, so it's unsurprising that he's being hounded out at the first sign of a crisis.