Also the architecture. You can throw as much horsepower as you can dream up at bad code and it won't scale.
My point is that Twitter has already optimized its code base, while others like Parler clearly haven't. That's why Parler needs loads of programmers and architects but Twitter really doesn't any more.
Twitter seems to work like an app or an online game, not a web page. It does most of its work in the user's browser and minimizes its communication with twitter servers. It is hard to square the competence evident in such optimized coding and sane architecture with the general insanity of the rest of twitter.
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