Cryptography Research patented quite a few DPA/SPA countermeasures, if there is a non obvious patent on Curve448 it will likely be one of those making it hard to make a non infringing, fast yet not vulnerable HW implementation... Given their business in licencing those countermeasure (https://www.rambus.com/security/dpa-countermeasures/licensed...), one can see their eagerness to get some curves in widely used standards as suspicious in that light.

I'm not really concerned but I also understand why one wouldn't implement anything Rambus related given their history of patent trolling...