Why big sites use 'bad practices'?
I often see articles, posts and comments something like:

 - globald are bad in javascript
 - script tags should be at bottom of page
 - css should be in external files and at the top of page
 - scripts should be in external files, not plain script-tags.
 - etc.

I've looked up html-sources of some big sites and have noticed that they have a lot of plain javascript and css inside html-markup. Also not always javascript and html is obfuscated. and so on.
Why big sites use 'bad practices'?
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I often see articles, posts and comments something like:

 - globald are bad in javascript
 - script tags should be at bottom of page
 - css should be in external files and at the top of page
 - scripts should be in external files, not plain script-tags.
 - etc.

I've looked up html-sources of some big sites and have noticed that they have a lot of plain javascript and css inside html-markup. Also not always javascript and html is obfuscated. and so on.