I'm going to let you in on a little secret as to why some people type in all CAPS. Most of them are not shouting.
They are just lazy.
They don't want to think through where to capitalize so they just go with all caps to make things easy for their simple and lazy brains.
When you type in all caps you don't have to worry about looking foolish by failing to capitalize proper nouns or words at the beginning of a sentence.
There! I'VE SAID IT!