I'll speak for the ones i've been dealing with (Pornhub.com, Brazzers.com, Keezmovies.com, XTube.com, and some other small ones).
Since i started at my company, i only did a website from scratch on one occasion (Videobash.com, not porn), and i think it was done right, it scales very well, using a framework we (me and an ex-colleague) designed and coded targeted for high traffic/high load needs. As for the other sites, i think people here summed it up pretty well, very often the decision are made by managers/marketing people, and we just can't spend the time we want to on optimization and good coding.
But, it's a situation that is starting to change, at least at my company, after a year or so of fighting, we finally started to rewrite all of our sites, using the proper technologies, structuring it correctly, using the framework that we did. You still have to keep in mind that the teams are very smalls, for example, Pornhub.com (17Millions visists/day, 3Billions+ pageviews per month) is maintained by 2 Programmers, and from time to time we can get our hands on an integrator, so understand that it's very hard to address all the issues. So even if, in the case of Pornhub, we were able to scale (since i joined this team) from 12Millions to 17Millions users with less hardware and better performance, i'm still far from being satisfied with the current state of the code.
But be sure, that personally i take the performance of my websites at heart. But there is also all the factors i can't control, advertisers to begin with, a lot of heavy crapy Flash/JavaScript.
Since i started at my company, i only did a website from scratch on one occasion (Videobash.com, not porn), and i think it was done right, it scales very well, using a framework we (me and an ex-colleague) designed and coded targeted for high traffic/high load needs. As for the other sites, i think people here summed it up pretty well, very often the decision are made by managers/marketing people, and we just can't spend the time we want to on optimization and good coding.
But, it's a situation that is starting to change, at least at my company, after a year or so of fighting, we finally started to rewrite all of our sites, using the proper technologies, structuring it correctly, using the framework that we did. You still have to keep in mind that the teams are very smalls, for example, Pornhub.com (17Millions visists/day, 3Billions+ pageviews per month) is maintained by 2 Programmers, and from time to time we can get our hands on an integrator, so understand that it's very hard to address all the issues. So even if, in the case of Pornhub, we were able to scale (since i joined this team) from 12Millions to 17Millions users with less hardware and better performance, i'm still far from being satisfied with the current state of the code.
But be sure, that personally i take the performance of my websites at heart. But there is also all the factors i can't control, advertisers to begin with, a lot of heavy crapy Flash/JavaScript.