Yep we should have scored. A couple of problems though - Taps was flat out after beating his marker. Harris and Cummins not after being caught flat. Never easy to hit a target in that situation but I believe the main reason was Harris line. Watch it again, he runs a terrible line, basically right next to and slightly behind Taps.
Taps straightened enough but Harris didn't make a decision whatsoever, neithe back inside or an outside line. I'd sayyid he gne inside Taps would have hit Cummins, had he gone to a decent outside line he'd have hit Harris.
In short I reckon he wanted or thought that it would be a shorter pass to either one in the scenario above. Harris fucked his line and that caused indecision and the moment was lost.
Another reason Harris isn't a 15s ass but yeah he should and normally would have passed. Ucharacteristic from Taps, that's what all these muppets don't understand whereas with Hirne the league player, that's his standard, a bit like AAC (Adam Ashley-Cooper).