Access to dozens of services that AWS offers, that you'd want to utilize entirely on their networks ideally. That service list is only going to keep expanding. The cost for Etsy to duplicate and maintain any of those, is high. AWS is also likely to be one of the leading platforms for AI services/tools, which Etsy will no doubt want to make heavy use of in the future; that's another expensive duplication effort if they do it all in-house.
Let's say AWS has 50 services today. Etsy won't have to duplicate any of those by building & maintaining their own versions. It's an extraordinarily time consuming and expensive process to do so. The capabilities AWS can enable will get greater, while the expense to replicate on your own what AWS can do, will also climb. The extrapolated result, is that AWS & the others will perpetually take market share for the next 10+ years from do it yourself approaches. More for the software duplication expense (time & money), than the hardware/bandwidth cost difference.
Let's say AWS has 50 services today. Etsy won't have to duplicate any of those by building & maintaining their own versions. It's an extraordinarily time consuming and expensive process to do so. The capabilities AWS can enable will get greater, while the expense to replicate on your own what AWS can do, will also climb. The extrapolated result, is that AWS & the others will perpetually take market share for the next 10+ years from do it yourself approaches. More for the software duplication expense (time & money), than the hardware/bandwidth cost difference.