I think it's because you're wearing your rationalist shoes.

The frequent bolding did make it hard to read. Also, changes in fonts like this are frequently a sign of crankiness so they likely bring up negative associations. People may also be downvoting for the post being in Main rather than Discussion. It is on the borderline of which of those one might reasonably put it- I suspect that the lack of sources/citations may push it more into the Discussion section.

I didn't downvote, but 1) I think this belongs in Discussion not Main, and 2) I would have expected an article with such a title to be about reasons to learn a new language -- you should have titled it “How to Learn a New Language” instead

I'd also recommend an introductory paragraph, where you explain what the post is going to be about, your basis for believing your information is correct, etc. Something like "this is a post describing a specific strategy for learning a new language. I've used it to learn Mandarin, French, Urdu, and Hindi." First because the opening is rather abrupt, and second because (as you can see) without citations everyone assumes you're working only from anecdotal evidence. If you aren't, you should definitely give your sources. And if you are, you should explicitly make that disclaimer, because otherwise it feels (at least, to me) like you're trying to make a stronger claim than just "hey, here's something that works for me."

My suggestion would be to add an introduction. There are many more things to be read than time to read. It's incumbent on you as a writer to convince people that what you have to say is worth the time investment. And you need to make that case clearly, convincingly, and concisely right at the beginning.

For this particular article, you need to establish two things:

• Why the reader should care about learning a foreign language. You take this as given, but I submit that it's not as obvious as you might think. It sometimes seems like everyone else in the world is trying to learn English - why shouldn't I let them do all the work?
• Why the reader should listen to your advice. As far as we know, you're just some random person on the internet. Even if I am interested in learning a foreign language, why should I trust your suggestions?

A paragraph or two addressing those two points would go a long way towards convincing your potential readers that your article is worth their time to read.

I didn't downvote or upvote you, but here's my feedback:

-I disagree that learning (non-english) languages has a high value/cost ratio. Thus, I'd rather not see the enthusiastic exhortation in the title (though I would be much less opposed to it if I thought that you were exhorting people to do something which actually did have high value/cost ratio.)

-I am fine with/appreciate the bolding, italics, and caps -- things that help me grok someone's emotions as they're writing something like this are appreciated, because it lets me get inside their head better.

-Citations would probably be appreciated on most things.

-This is unlikely to be generalizable to most of your audience, but I really don't like things that require brute mental force -- they don't hold my attention.

I can scarcely imagine myself being fired up enough about something to use that much emphasis, so it seems unlikely your "get super motivated!!!" strategy will be very useful for me.