How they did it: economy of scale, and mingling businesses.
Google had the infrastructure, expertise, experience, and an army of top tier coders to execute on any engineering challenger, all of that even before it acquired YouTube.
Google is mainly an ads business. An expertise edge not only in engineering at large scale, but also in the delivery of web ads. And, given their ads business perform on profiling people, YouTube consumption habits feed the rest of the beast.
If these didn't skip your kind, yet still wondering how did they do it, the following were crucial to make Google unique in their ability to succeed with YouTube (and the rest)
- An engineering first company. They hire wagons of product people and managers, but when things don't turn out positive they switch back to their roots. As an anecdote, on day the CEO felt things were going south. Fired all (probably just most) managers and tasked engineers to figure things out.
- A coherent vision. Google doesn't jump on where's the hype. Their position in A.I recently perhaps couldn't resist the pressure. It sticks to the core competencies while building experimental products on green fields that fit in growing the core business.
- Long term. Clearly Google has so far resisted to make a quick buck. The no evil slogan is gone, but the spirit remain in building long term value. That kept them from tarnishing their reputation while reaping the amounts of profits once everyone could only swear by their products (mail, drive, YouTube, of course search, Android thriving as now the only remaining competitor to iOS, if any other company had acquired Android in that shape when Google swooped it, it would have given up on it seeing how long the road was about to take to make it a viable mobile consumer product)
How did they do it? Google is in the top 5 of all companies that have ever existed. Takes more than a genius and plenty of humbleness to achieve this feat.