I feel like trying properly to explain it would veer more into speculating-about-his-psychology than I really want to. But it doesn’t seem totally inexplicable to me, and I’d imagine that an explanation might look something like:
Eric doesn’t think it’s his comparative advantage to answer these questions; he also sometimes experiences people raising them as distracting from the core messages he is trying to convey.
(To be clear, I’m not claiming that this is what is happening; I’m just trying to explain why it doesn’t feel in-principle inexplicable to me.)
I take this to be pretty strong evidence that this is not a good article for people reading Drexler to start with! (FWIW I valued reading it, but I’m now realising that the value I got was largely in understanding a bit better how Eric’s sweep of ideas connect, and perhaps that wouldn’t have been available to me if I hadn’t had the background context.)