Would mainly make sense if I returned the original order, otherwise there must be much more efficient use of the recommendation space.

Well, no there isn't, and this company has the best data available on the planet to prove it.

There should be a corollary to Hanlon's Razor. Something like, "Don't attribute to genius that which is adequately explained by laziness."

Frankly, calling it Bezos's Razor would be very appropriate, because that's basically how the whole Amazon storefront works.

Not quite. ML algorithms that continuously crunch billions of data points don't need to be called "genius", they're simply way more exhaustive in their search of optimums than "a vague idea from a regular person on the Internet that the best reaction to such situation is to do x" (with absolutely zero evidence to show for it of course).

AIUI, recommendations can come from multiple providers. If very detailed recommendations that take into account the fact that you’ve already bought a vacuum timeout, then your recommendations come from a dumber provider that is based on recent searches.

By “provider”, do you mean internal Amazon recommendation services?