Anyone can bake a cake. It's a lot harder to bake a billion cakes.

But baking cakes scales horizontally, just buy 10 million bakeries and hire 20 million bakers. You don't need a baking engineer to reinvent the oven, especially if that'll potentially end up costing you more in the long run.

Throwing away the metaphor, IMO horizontal scaling is sometimes cheaper then vertical scaling.

Yes, but if you have 10 million bakeries, you can afford a team of 10 software engineers to increase your efficiency to produce the same output with 7 million bakeries and 10 million bakers.

I'm sure it's far more than Crud. Access control, analytics, filtering, probably some pseudo-science, etc.

Also they run ads