I don't know, but I have what I think is a reasonable guess.
First, if separation (wake turbulence mitigation) was the reason, then why would ATC block a perfectly servicable runway by having an aircraft line up and just sit there for upwards of 10 minutes? It would make far more sense to have the aircraft taxi and hold short of the runway, than to line up and wait, until there is a likely large enough gap in the traffic. Even if the first aircraft is holding short at the threshold of 16, unable to take off due to say separation concerns, it would still be possible to allow another aircraft to enter the runway from the next taxiway down, backtrack then line up, or to land on 16, if ATC wants to do so. (I would argue that this is probably inappropriate for other reasons, but at least the takeoff scenario looks no more complex than would be a takeoff on 14.)
Second, notice that 10/28 and 16/34 intersect at about a third of the runway from one end. (A third down the runway on 10 and 34, two thirds down the runway on 16 and 28.) Even not considering winds, this would severely limit ATC's ability to safely use those two runways simultaneously, especially for heavier airplanes, as they would need to consider also the situation at the intersection in the case of a successful or a rejected takeoff or, in the case of a landing, an airplane either landing long or executing a missed approach. All of these add complexity and risk.
The ATC mantra is safe, orderly, expedient, in that order. Safety comes first, so anything that compromises safety in the name of expediency is going to be a no-go from the start.
If the airplane was "well behind" its scheduled departure time, yet just sits on the runway for a good ten minutes, my first guess would be that whatever caused the initial delay might be causing further delay before the pilots feel comfortable beginning their takeoff roll, or before ATC clears them to begin the takeoff roll.
As an aside, engines don't cause wake turbulence per se; wings providing significant lift do.