You don't think the military would be interested in a Un-identified target doing 450kts at 29,500' ( not a common Airline level ) flying smack across their country???
I tell you what, if that happened over the Ocean and this target approached an US navy Battle group they would get detected 200 nm out, tracked, intercepted, identified visually and then shot down if they didn't turn away from the Carrier. ALL USING PRIMARY SEARCH RADARS.
Just because the Malaysian Air Force was asleep at 2 am and didn't notice at the time does not mean that Primary Radar is useless and not needed.
And yes I'm aware civilian ATC don't use Primary Radar these days thanks all the same.