Where do you see this happening? Can you give some more context?

English is not my native language, but I come in contact with it on a daily basis. [Internet, work, etc] I've seen writing in English from many native and non-native speakers and never seen (as far as I remember) anyone do this. Apart maybe for stylistic reasons in titles of books or movies (generally they then don't capitilize the smaller gramatical words like 'of', 'and', 'the' etc).

The only thing that comes to mind is that maybe you've specifically met people who speak the same language in which they capitalize every word, so they copied it in English. Like in German all nouns are capitalized, so I can imagine some Germans sometimes making the mistake of capitalizing words in English that normally aren't capitalized in English.