I very much agree with what you've written — I think another factor may be that many bloggers mimic styles of writing with which they're familiar, e.g. newspaper-style journalism.
You're post also reminds me of one of my favorite Virginia Woolf quotes:
Of all forms of literature, however, the essay is the one which least calls for the use of long words. The principle which controls it is simply that it should give pleasure; the desire which impels us when we take it from the shelf is simply to receive pleasure. Everything in an essay must be subdued to that end. It should lay us under a spell with its first word, and we should only wake, refreshed, with its last.
— Virginia Woolf, The Modern Essay
Do you think blogs are a bit like essays as Woolf has described them?