Setting up your own servers was not a bottleneck to the generation of internet companies that preceded AWS, and time has only made hardware cheaper, bandwidth more affordable, and OSS higher quality and more plentiful. It is easier than ever to host your own services, AWS just makes it cheaper up front thanks to their massive scale.
Point being, people aren't choosing AWS because AWS solves a problem they're incapable of solving, people are choosing AWS for pricing flexibility and faster time to market.
So when you say "what AWS does was previously done by every single IT department at every company across the globe" yes sure but (1) it was done worse in many cases, with data loss or significant downtime, and (2) there were fewer such companies by magnitudes, because of the cost barrier.
What AWS did was take a costly process, done inconsistently and to varying degrees of correctness across the business world, and make it available to everyone at a very high quality, with a innovative pricing schedule.