To be fair Frank, have you forgotten the array of LPFs we had on preamplifiers and integrated amplifiers back in the day? We had defeatable low (and high) filters for at least three reasons:
1: the filters were not just for the sole use of the phono stage- often open reel, tuners, cassette decks all needed the use of them.
2: the placement of the filters was mostly always after the phono stage.
3: ganging up several different analogue filters results in additional gain stages to keep levels the same.
So we had the correctly designed RIAA stage itself AND switchable susbsonic/15Hz/30Hz//low/70Hz/defeat etc. Sometimes to get rid of excess woofer movement, preventing feedback, knocking down hum or even idler wheel noises. And in tape we had head 'woodles' to kill, mains hum etc. Filters to target what we wanted to without wrecking the music from various sources.
Example Spec1:
View attachment 305647
This is just a single use phono MC stage, and so the manufacturer has implemented what looks to be a very sensible infrasonic filter, I agree.