Once you are at a 100 millions customers company, the urgency becomes to ban all these MySQL and postgre for production systems. Or you need to figure out how to seriously handle a multi master setup in production.

There are the 80% bottom of companies who are just toying around doing small products and MVP, that should stick to what's easy.

There are the 5% at the top who are guaranteed to get 1 million customers no matter what they ship, that should stick to doing things right and sustainable from the start.

Contrary to what the other comment state: sharding and failover are ALWAYS the EASIER choice at scale. The alternative is to be unable to change hardware/systems and to be forced into 15 hours downtime window for every maintenance/upgrade operation, which is a huge liability when you have real users.

The 2 types of companies have opposite priorities.