It's not horrible, but it just takes too long to learn as an auxiliary language. Just as the most powerful software usually loses market share to the easiest.
English is far from the easiest though. It's one of the most difficult languages for non-native speakers to learn. The grammar, pronunciation and vocabulary is too inconsistent and large.
Spanish is a much easier language. It has clear pronunciation rules, a more limited latin-based vocabulary and few grammar exceptions.
> It's one of the most difficult languages for non-native speakers to learn.
It's really not that hard. The sheer amount of media available in English makes it easier to learn than the languages where you have to specifically seek out texts written by native speakers. The fact that it's very analytic [1] is also helpful. I found Spanish harder because the numerous verb conjugations are too difficult to remember. My native language's conjugations are even harder, but luckily I've been learning it since I was a baby.
>The sheer amount of media available in English makes it easier to learn than the languages where you have to specifically seek out texts written by native speakers
It seems that way because you only look or notice English content.
Because it's often the best content available for any given topic. If I had any reason to specifically seek out Spanish, French, German content I'd probably be a little better at these.
Spanish is a much easier language. It has clear pronunciation rules, a more limited latin-based vocabulary and few grammar exceptions.