[makestuff]

Tons of marketing/advertising. The free GrubHub+ subscription through prime probably burned through a lot of cash. I doubt Amazon was paying them very much (if anything) to Grubhub. Then you have all of the corporate staff (around 3k based on google search) who are highly paid.

[SoftTalker]

And the competition from UberEats and Doordash, who also are constantly promoting discounts, free orders, etc. so there's almost no way they can recoup actual costs let alone turn a profit.