Objective-C never caught on outside of the Apple/NeXT ecosystem because its biggest advantages were in the application frameworks, not the language itself. By the time iOS made Objective-C popular there were entrenched alternatives in the C++, Java, and .NET ecosystems. Swift is facing the same challenges, but against a newer generation of competitors that are much less established. It's probably still an uphill battle for Swift to gain outside adoption, but it's not climbing a cliff.