Because you are trying to use the equipment in a fashion for which it is not designed.
You have a sinple, free, easy solution to this trivial issue. Why not use it?
Of course whining works, too. 
It makes sense for triggers to go downstream.
I have not seen equipment where one can switch a trigger between send a receive. But such equipment may exist.
The P10 and P15 have in and out triggers. When I had my mk 1 DSD DAC I used tge P 10 to turn my amp on and off. This was before I got the BHK Preamp.
Cool.
Having both send and receive could be useful.
Is anyone using the trigger output successfully? Just plugging a trigger cable into my unit causes the display to flash erratically. Thanks.
Mine does something similar, but only found that out recently when my preamp was acting up. Tried to turn the BHK 250 off/on with the DAC trigger, but the display was acting like the DS was rebooting repeatedly. Didn’t like that so I didn’t use the trigger. I got my preamp straightened out (the trigger works great on it) so not a problem any more. Surprisingly it appears the DAC triggers are not active yet, this is a simple thing to implement (right?) so why isn’t it working?