The Menzel guy kind of address that at the end, though I wish he went into more detail.
My guess is his attitude is why use less tested technology when the capacity of the Ka band link does the job dependably.
As more probes go up and antenna time grows shorter, increasing link capacity will become more necessary. Until then, why experiment on a 10 billion dollar project?
I agree for JWT optics was not really an option, however moving forward many space missions will start to use optics. Last year NASA launched the Laser Communications Relay Demonstration and there are extensive plans for integrating logical links into the DSN
My guess is his attitude is why use less tested technology when the capacity of the Ka band link does the job dependably.
As more probes go up and antenna time grows shorter, increasing link capacity will become more necessary. Until then, why experiment on a 10 billion dollar project?