Why would the expectation of privacy be different depending on which spectrum of light the information was captured in (visible vs radio)?

In both scenarios, the data is held by a private third party and a person generates this data pretty much by-default.

This is the relevant bit:

In Carpenter, this Court held that accessing cell-site location information (CSLI) constitutes a Fourth Amendment search because “individuals have a reasonable expectation of privacy in the whole of their physical movements,” 585 U. S., at 310. The Court reasoned that CSLI provides a “detailed” and “encyclopedic” portrait of a person’s whereabouts, id., at 309, and, with that, “an intimate window into a person’s life,” id., at 311. Because people “compulsively carry” their cell phones “all the time,” the Court explained, a cell phone “tracks nearly exactly the movements of its owner,” and thus “faithfully follows” him not only through “public thoroughfares [but] into private residences, doctor’s offices, political headquarters, and other potentially revealing locales.”

This question seems preposterous on its face. If you walk around in public wearing a t-shirt with text on it, there's a reasonable expectation that people will read it. Specifically because it reflects light.

Chatrie was about Google’s personal location tracking feature in Android, not about carrier tower records.