I'm not an expert, and I'm certainly not trying to argue, especially not with someone who knows more than I do.
I thought the issue with climbing on amsteel was friction. It's slippery, and hollow, and melts if it gets too much friction. As I understand it, RescTech and some other climbing ropes have (essentially) Amsteel cores, with nylon or polyester or Technora jackets. If I've got that wrong, or am overly generalizing, then I'm happy to be corrected. But we're discussing bridges, not climbing lines, so I'm not sure the dearth of pure dyneema climbing ropes means that it's not suitable for other climbing applications, such as slings or quickdraws or soft shackles or other rigging. A bridge generally isn't moving very much; at least, not in comparison to belaying a climber, so it's not going to melt from friction. As long as it's properly constructed and attached - and, considering how popular they are, I'm persuaded that there is a proper way to construct and attach an Amsteel bridge - what exactly is the issue?
I can't recall the name, but there is/was a climbing rope that proved to be poorly suited to bridges. IIRC, the repeated pressure in the center of the bridge crushed the core, weakening it to the point it was unsafe. So the thought occurs to me that just because something is an excellent climbing rope doesn't mean it would make a good bridge, and it might not be a good idea to climb on every suitable bridge material. Am I missing something?