Essa pergunta jã foi feita varias vezes aos devs do friendica/red, e eu, como  vi alguém outro dia  fazendo a mesma  pergunta  novamente nas redes diaspora e friendica,  abusei da paciência deles  e fiz novamente essa pergunta :).

Espero com isso  esclarecer uma vez por todas essa questão.

"You choose a language for the task at hand based on what you wish to accomplish and the environment where that software is going to be used. This involves not only the software environment but the complete environment - software, hardware and user base. I chose php for a number of reasons. Rapid protoyping is essential for developing innovative platforms. The number of existing PHP developers is ten times, no a hundred times, no even more - than for any other web-based platform. This is critical for an open source project. At the same time, the blogging craze started to die off and left huge amounts of unused shared hosting capacity around the planet. I thought this would be a great way to make use of all that spare capacity and the skills of hundreds of thousands of existing LAMP admins. This didn't all play out the way I originally planned, but those are the reasons I chose this platform. Ruby is still a bit of a boutique platform. Not a lot of people are good at it. The hosting community has been slow to adopt it. This isn't reflective on the language and its capabilities - I'm only considering the environment where these webapps need to live. This kind of a project needs to be accessible to all levels of skills, something WordPress proved could be done if you used a commodity stack. There are even "newer" technologies like node.js. They currently don't have the rich set of libraries and utilities to create a project of this scope without a lot of devs working on various aspects of it - just to give it the support infrastructure required to develop rich applications quickly. We don't have the luxury of lots of devs. Several other language platforms were considered and ruled out for other similar reasons. They are great technologies, but commodity webapp environments aren't their strength."

Um outro  dev respondeu: "It's kinda like asking "Why is this Playstation game written for the Playstation?" That's just what the world uses. Commodity hosting uses a LAMP stack. If you use something else for a decentralised service that has to run on commodity hosting, you're an idiot. End of discussion. I suppose you could stretch it out by adding that PHP is good for prototyping, and there's a case to be made for rewriting the whole thing in C later. I suspect you're actually remembering threads about why Ruby developers don't like PHP - but why they don't use it is a very different question to why we do. Basically, they invented an urban myth that PHP is inherently insecure, and that's where most bugs are. There are lots of threads pointing out that, actually, that's complete bullshit. Most bugs are in C, and vulnerabilities are almost always in bad code (like Diaspora), not bad languages (like PHP) anyway. Here's a test - try to get a private photograph from Diaspora (I'll give you a hint - just fusk one), and try to get a private photograph from Red (I'll give you a hint - forget trying to hack your way in, you'll only do it by finding an admin, and hitting him with a wrench - unless it's E2EE, in which case, you'll have to find the owners and hit them with a wrench)." Commodity hosting uses a LAMP stack.

E por aqui termino ;-).