It's like saying it's more important that the car drives reliably rather than everyone that needs to travel fitting into the car in the first place.
When this is the case, you probably have enough money to hire someone who knows what they're doing with databases in order to set up a migration properly - you don't really need the ease of use configuration features.
SQL databases give data durability and transactions, integrity constraints, joins etc, which makes writing software a simpler experience (with a smaller chance of corrupting your data etc) which is generally a nice property to have when you're a small company that's moving fast and breaking things.
Naturally, there are plenty of people who do need to scale a lot, too, but presumably by the time they need to, they have a good idea of the problem and exactly how best to scale it.
Replication is not very easy to setup in PGSQL. Sure, I can do it, but our product is an on-prem product that our users are responsible for configuring and maintaining. Having them configure PGSQL replication would be something they're not willing to do. MongoDB's configuration of replica sets is quite trivial compared to PGSQLs.
I bring this up every time someone says "PGSQL > MongoDB", even on PGSQL threads where PGSQL devs participate and they admit it's not quite there yet, but that they're working on it.
And all that said, it is getting demonstrably better to configure replication in PGSQL, so it's going to get there some day and I can't wait.
Do you have a link to such a thread where pgsql devs admit its inferiority?
Also, if you take a look at perf when running PG on for example Azure or EC2, you will realize that IO is pretty slow but nodes are cheap. So you want to scale out early.
Running stuff on a single machine sounds like a perfect single point of failure to me. The actual size of the data does not affect wheter single point of failures are acceptable in a business.
I've seen so many people recommend PGSQL, saying its very simple, but when actually asked about how to set up a simple cluster which fulfills the absolutely basic requirements, then everyone just responds somethin similar to what you wrote. I find it very annoying to be honest.
