Missed? No, they are right there in the report. Ie, technologies that we do not have, which would individually be a major NASA program, and which are the minimum requirement for a space elevator of any type. (The robotic repair systems alone are probably beyond the current state of the art of robotics, IMO. But the ground station, the "tramway" tower construction (let alone ISRU fabrication), the L1 ribbon deployment system, the actual elevator "cars", even the single use "tramway" cable tow-vehicle, etc etc etc. Possibly within current technological limits, but each hideously expensive to develop.)
A single 1km lunar tower construction would be the largest (and most expensive) project NASA has even done, even if the parts were already sitting in crates on the lunar surface. Pearson needs over 50 of them (more if they are smaller). And they are a small side-part of his proposal.
Likewise, a lunar facility which could produce tower-parts from lunar materials would be the most technologically advanced research project NASA has attempted in decades, even without the actual construction of towers. Much more demanding than anything going on at the $3b/yr ISS, or any of the $3b/yr SLS development, or the $9b JWST. And that's just something capable of taking regolith and outputting a small number of tower components; not something capable of actually producing a full 1km tower's-worth, let alone 50+. Just being able to produce the required types of parts at all. And ignoring that it has to be mobile and capable to tracking from the equator to the poles. (Or have a fleet of delivery vehicles capable of relaying parts to and from the construction sites. Each of which would be the largest and most advanced vehicles ever produced by NASA. Making the Mars Curiosity rover look like a toy.)
There's probably a thousand other technologies of similar difficulty and expense that I'm missing, too. These few just jumped out at me. Components which would individually be multi-decade multi-$billion/yr Agency-wide flagship programs. The 180,000km ribbon itself is beyond me to even speculate over the difficulty or cost, plus the ribbon's deployment system...
It's the difference in the definition of "Feasible". A lot of impossible/difficult/expensive proposals are deemed "feasible" by NASA standards. "No show-stoppers" as they say. Venture Star was "feasible", NASP was "feasible", Freedom Space Station was "feasible". Hell, SLS is considered not just "feasible" but "low-risk". Similar reports in the seventies of giant space-stations (Stanford Torus, Bernal sphere, or O'Neill cylinders) were considered "technologically feasible". And they likewise required impossibly huge projects as small sub-sets of their development (such as mining, processing, and giant mass drivers on the moon just to supply the raw materials for their construction.)
Pearson's elevator, while simpler than an O'Neill cylinder, would nonetheless make the Apollo program look like NASA's Christmas video.
[Aside: My throw-away comment in last post "or the sort of autonomous in-situ manufacturing that would have already replaced the entire manufacturing industry on Earth" is unclear. I meant if you had the technology to automate the construction of 1km lunar towers from nothing but lunar regolith and solar power, the same technology would have already revolutionised and replaced the majority of manufacturing and especially construction if used here on Earth. Imagine being able to construct, say, concrete and steel buildings or bridges by feeding iron ore, limestone, coke, water, etc, into an automated (solar powered) construction system.
Further aside: BTW, we should be developing lunar and asteroidal ISRU technologies. But proposing a giant space project which treats this radical and revolutionary technological advance as if it's already proven and mature... Hence, "you have to have an industry in place in space so large that you must have already solved the problem you are trying to solve with a space elevator."]