I'm pretty sure McCain wouldn't have started his presidency by bowing down to ME leaders, showing submission.
Things like that actually matter in the ME. Strength is admired, weakness is despised. And Oboso has made it a point to highlight weakness.
And whether you like it or not, a South Korean civilian jet is not a US ambassador. With the former, you look at what would be in the best interests of the US, in the latter, the best interest of the US is ALWAYS a forceful response.