Not all clouds are the same
Possibly true for AWS. Not sure, don't use them.
Some of the things cloud providers are doing though you just cannot build on premise. Look at Google Cloud Platform. Google uses a 2 petabit/s (yes, petabit) interconnect network in their data centers. You can't buy that on your own from Cisco or Juniper. It was invented by Google. Google owns the world's largest IP network with 200 or so PoPs and caching data centers in every corner of the world (why YouTube videos don't need to buffer). You can't do that on your own unless you want to start laying transoceanic cables. Google uses custom hardware tip to toe for security and cost reasons. You can't do that... or at least not at a reasonable cost.
Also, one of the biggest advantages of cloud is that you pay for actual utilization in near real time, not your once every year peaks. That can be huge. If you are a retailer building out infrastructure because on Black Friday your workload is 10x the average, you have a ton of infrastructure idle most of the year. You never really know where your peak will be either so it is just common practice in infrastructure sizing to take what you think you'll need and add 20%. You don't need to do that in cloud.
Biting the hand that feeds IT
