This also puzzles me. If I buy a household appliance that's not a consumable product (most shouldn't be), why does it recommend more of the exact same? Why doesn't it instead recommend other types of appliances?
The key take-away should be that you're comfortable with buying household appliances online, usually not that you need another vacuum cleaner within the next year.
It's data, and a lack thereof. It's easy to know you're browsing a site. It's almost impossible to know you bought something.
Banks and merchants and publishers and advertisers and all the layers in between create dozens of data silos and nobody is interested in sharing. Add to that the weird expectation that people don't want to be tracked but yet want adtech to know when you've bought something.
The key take-away should be that you're comfortable with buying household appliances online, usually not that you need another vacuum cleaner within the next year.