And also, while a groupset might indeed cost $1000, what sort of circumstances might require one to replace the entire groupset?

(We're talking repairs rather than upgrades.)

A chain for a high end group (like a XX1 Eagle) is 80$. A replacement cassette - that you will need after 2-3 chains is 300-500$.

And if you are into mountainbiking - there is also a fair amount of chance you might break something like a derailleur and spend a few hundred to fix that.

Riding 50k km on dust/gravel roads, and the frame and wheels will still be good but chain and groupset will be significantly worn.

Chain is indeed a wear item. It costs tens of dollars to replace.

$1000 groupsets simply don't deteriorate in the manner you describe. Source: I rode many thousands of kilometers on my gravel/adventure bike, including a 1000km ride around Kenya (very dusty, rocky roads where there are roads). The only two groupset components I needed to replace on this 2016 bike so far were the derailleur hanger and a jockey wheel. The former got bent due to carelessness on my part and could have been straightened, but I chose to replace it for structural reasons. The bearing in the latter got a little sticky and so I replaced the jockey wheel.

Each of the two parts cost the equivalent of US$15 here in the UK.

I think this is a very long way from replacing the entire $1000 groupset, which was what the post I was replying to suggested.

I believe the new 11s/12s with their higher chain angles tend to wear faster. They actually recommend changing it with the chain.

I think we're talking about different things.

I am talking about the groupset (the shifters, brake levers, brake calipers, derailleurs, crankset, bottom bracket, chain and cassette).

There are indeed some wear items (chain; cassette, especially if the chain isn't replaced when worn; brake pads; brake rotors) but, apart from those, a looked-after quality groupset can last decades.