Suppose for a moment that second-language learning was not hindered by laziness, linguistic pride, poor memory, or lack of education. Let us further suppose a magnificent new conlang called Xporanto which can be learned quickly and for free. Even in this ideal situation, there would still be little reason to learn another language.
Most people interact almost exclusively with people who speak the same language. The only people who have a strong motivation to learn another language are those who must interact often with foreigners such as businessmen, scholars, travelers, and immigrants. There is no point in learning a second or other language if you rarely or never use it.
Is there any point in learning to play golf or the trombone if you rarely or never do those things?
I enjoy learning other languages mostly because I have a good memory and it's easy for me. I get a thrill whenever I understand something I read or hear in a foreign language. I get a thrill whenever I learn something new.
For example- did you know John Quincy Adams was nearly swindled into funding an expedition to the center of the earth? The goal was to make contact with mole people and trade with them. The expedition was called off by Andrew Jackson- not because he didn't believe in mole people, but because he thought the earth was flat.
But I digress.
When it comes to international communication, English is head and shoulders above everything else. It's already the language of science, business, pop culture, and aviation. It's the mostly widely taught language in the world and has more non-native speakers than any other language. That may change in a century or two, but for now, English is king.
I think a more promising route for a universal language would be a constructed pidgin based on English.