@MMScotofGlasgow, Hopefully it’s not too late…
Francis Yates discusses Petrus Ramus as an educational reformer in Chapter 10 and onward in The Art of Memory. There she outlines Ramus’ crusade against images (based in part on the admonition from 4 Deuteronomy about graven images) and on their prurient use (sex, violence, etc.) which were meant to make things more memorable. Ramism caught on in the late 1500’s and essentially removed memory by the root from the subject of rhetoric of which it had been an integral part. Ramus felt that structure and rote memorization would suffice in its stead. As a result the method of loci decreased in prominence in schools and disappeared from the scene based on educational reform which was primarily pushed by Huguenot/Protestants. I’ve not read anywhere that the practice was ever banned, it just fell out of fashion due to these reforms.
I’m sure it didn’t help that printed books became ever cheaper during/after this time and so the prior need to memorize for those reasons wasn’t helped either.
I’m sure another confounding factor was Erasmus’ Copia: Foundations of the Abundant Style (1512) which dramatically popularized the keeping and use of commonplace books by the learned and literate. These became a regular place in which people collected and kept their thoughts and ideas rather than memorizing them as they may have done in the past.