I think you're massively underselling how complex it is to run something at scale. It's not a matter of just making the database go fast. Just using the databas

I think you're massively underselling how complex it is to run something at scale. It's not a matter of just making the database go fast. Just using the database as an example (even though there's way more to it than just the database), you can scale a database a bit by sharding or running it as a cluster or what-have-you, but you can only shard so wide before you run into other problems which are much harder to solve. Running at a massive scale requires rearchitecting almost everything that came before.