I'm also cringing over this. I wondered for a moment if there was a sudden desperate need to raise money, but I think the amount involved won't be enough to matter. I guess there is not much point in asking RMS what is going on.
Insurance of collectables is an expense. The more items go up in value, the higher the insurance premiums.
Because the artifacts are not critical to FSF's core mission, raising and spending donations to insure them might not be the best use of limited resources.
The linked XKCD's are #225 "Open Source" and #239 "Blagofaire" (the one with Cory Doctorow in a hot-air-balloon). Stallman-with-a-katana also shows up in the five-part arc #341-345 "1337". (I don't know if there were others?)
Selling off foundational relics to private bidders is imho a sign that an organization is done.