This immediately jumped out at me, the rest of the article notwithstanding. My hot take is that there are at least two strong reasons why it's so difficult:
1. You're not serious about it.
There's a man in my weekly French meetup who when I joined was a little bit better than me (which wasn't saying much -- I was horrible). Since then, his French has improved almost none. He can't conjugate, he can't pronounce, he can't even stay in the language: stumbling halfway through a simple sentence, he just gives up and switches to English. He's not serious about trying to improve. For him, I think, he just likes the social aspect of the group.
2. You worried about failing.
Far too many people I've seen want to be fluent to the detriment of becoming fluent. When in conversation, they think very carefully about what they say, practice pronunciation in their head, etc. Saying something embarrassing or even just slightly off is seen as a hindrance to their goals, but it's just the opposite: you have to make mistakes in order to get better.
Not to say that it's not hard to learn a language, but I've talked with so many people who just say, "Learn Spanish? At my age?! Impossible." But I can get by pretty well by myself in France with patient native speakers, and I'm self-taught. It's not as hard as people think.