Most of the companies that we work with actually aren't in SF either.
Think of it as an AWS analogue. If you are a company running some large predictable number of servers with a constant load, it's probably cheapest to just have a rack of servers, if the scale can cover the people to maintain them. If you have varying loads across different days and seasons though, AWS might make a lot of sense since you don't have to pay for servers sitting around idle. That flexibility comes at a premium.
To take it a step further, if you're a slightly smaller company that values time and agility and doesn't have a large dev ops team in-house, you might want to use a PaaS, like Heroku.
Think of it as an AWS analogue. If you are a company running some large predictable number of servers with a constant load, it's probably cheapest to just have a rack of servers, if the scale can cover the people to maintain them. If you have varying loads across different days and seasons though, AWS might make a lot of sense since you don't have to pay for servers sitting around idle. That flexibility comes at a premium.
To take it a step further, if you're a slightly smaller company that values time and agility and doesn't have a large dev ops team in-house, you might want to use a PaaS, like Heroku.