Looking at examples online, it is surprisingly easy to understand! I can see it being better than Esperanto for romance language speakers specifically, but it still seems to me like Esperanto would be a better auxiliary language due to the simpler grammar rules and no fixed word order

TBH I don’t know much about other auxlangs/conlangs besides Esperanto. What makes you prefer Interlingua?

If you mean “is Esperanto English”, the answer is no, they’re pretty different, Esperanto combines elements of latin and slavic languages. If you mean “Isn’t English already an auxiliary language”, the answer is also no. English is a lingua franca, not an auxiliary language.

Reading through this thread really makes me wish Esperanto or some other auxiliary language caught on

Perhaps you just haven’t found anyone worth interacting with?