From an advertisers perspective the purchase intent of a person who has already purchased a thing (even a thing you don't normally purchase more than one of) is very very high.
Essentially ads can have two different purposes - to make you aware of a thing (isn't IKEA great) or to make you do a thing (buy new cabinet doors). Both kinds of ads perform better at both if you've recently purchased.
When you purchase something you have more of an association to it, and are more likely to notice it's ad. Which strengthens it's awareness effect.
When you purchase something you are much more likely to think purchasing it is worthwhile (even if you haven't received it yet) so are much more likely to either purchase more for yourself or for others if prompted, where you wouldn't if not.
It doesn't take much for that purchase intent to be worth a cent more than any other random mcguffin.
How does this work for holiday, tractors and coffins? Well seeing the holiday you just booked makes it massively more likely you'll click the ad and search and purchase a different holiday for later in the year.
For tractors - same thing. You carefully planned and bought one that you're convinced is great, now you'll see your good decision and go back and grab another - or maybe add a bailer or get some quads from the same place.
For coffins. You were choosing between two, you bought one, now you'll click on it and upsell yourself.
Notably the item you clicked previously is most likely to be bought again, but your intent is best transferred to another product by showing you the product you bought rather than guessing which other product you'd want.
Humans are stupid and fail to make logical decisions, instead they reinforce and justify their previous ones.
Isn't the point of those, that in the end, the likelihood of you buying something again just recently bought might be tiny, but is probably still bigger than showing the same add to a random other person?