I know that you can't know everything, but I do wish people would ask for clarifications before judging. So, I'll pretend that you asked "Why are there talk/meta/pictures/dictionary etc., when these are obvious drain on resources", and answer that.
Meta pages (name starting with wikipedia:) are just ordinary wikipedia pages with yellow background, living in a separate namespace. There's a lot of stuff to write about the encyclopaedia that you don't want in the main article space.
Pictures are obviously needed. Come on.
Wikis for dictionary, quotes, textbooks were established when it became clear that people find Wikipedia's wiki to be a great tool for those and started massively inserting them into the encyclopaedia. It was decided that it's undesirable to have them in the main encyclopedia, so separate wikis were setup for them. They're really nice projects and their resource use is negligent compared to encyclopaedias.
There is no chat.
Talk pages are essential to the process of writing the articles. It's where people ask questions, comment on the articles, discuss their opposing views, etc. all without fouling the articles themselves. They are also used for working out policy before it's posted to wikipedia: meta pages. There are also communal talk pages, the reference desk (for help with writing content)and the village pump (for general community discussion).
Talk pages are again normal wikipedia pages, with a yellow background, and one can be created for any artcle or meta page. Implementing talk as a blog (instead of a wiki page with full revision history) would save resources, especially for the communal talk pages, which I estimate to represent 5 to 10% of the whole database size.
But, it may not be worth it. There is not much discussion of wikipedia. I'd say wikipedia (despite being on par with slashdot or sun, trafficwise) produces less discussion then Kuro5hin. People don't go there to chat, they go to write an encyclopaedia. General discussion is discouraged.
Wiki format also has many advantages for discussion: you can correct your typoes or wording, delete your comments, delete other peoples comments (if offensive or when archiving), you have a common blackboard for ironing out text or policy, etc. And, since revision history is kept, no text is ever lost and every deleted comment can be reviewed by anybody.
I don't know whether it's the common goal or the wiki format of discussion, but people on wikipedia are much nicer to each other than on your normal blog. I would never start a comment on wikipedia with a rant like the one above.
_Note_ that some content *is* permanently deleted - copyright violations, articles with no meaningful content, created by vandals or inadvertently created by readers, are quickly removed after review. Articles with no encyclopaedic value are removed after a 5-day procedure, involving discussion and attemts to rescue useful information. A large part of requests for deletion is turned down and articles are improved instead.
I mean, if coal can be converted to energy, then couldn't diamonds?
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