I'm not saying it's easy but it's easier. Different cloud services let someone else take care of replacing faulty hardware, upgrading hardware, adding new servers, software updates, backups etc. It's very difficult and time consuming to replicate all this reliably with a couple of dev ops guys.
If you rent dedicated boxes you don't have to worry about replacing hardware or adding new servers. Also the cost savings are so huge, as someone else stated a dedicated box could be 1/7 the monthly price of an equally specced AWS instance you can easily have a 1-2 devops guys on call and still save a lot of money.
I don't see where buying/colo makes sense though, maybe if you have a really huge operation going on.
Hetzner offers a i7 Skylake QuadCore 6700, 64GB Ram, 512GB SSD Raid1 for 60 EUR/month, an equally specced AWS instance (or multiple smaller ones) would easily be >400 EUR even when using upfront payment and reserved instances. That difference is huge if we are talking about 10-50 of these machines. The only benefit i see is when you can scale your app up and down a lot during the day to save costs, but i'd still like to see a real world case where that actually saves money. I am pretty sure most companies use AWS for the convienence and just don't care about the cost because it's minor in the grand scheme of things, like super popular startups with huge funding and years to figure out and optimize profitability.
