When Apple’s Swift language for MacOS and iOS development debuted in June 2014 as the modern successor to Objective-C, Swift began to gain a foothold with developers. But now Swift is actually slipping in popularity, according the latest Tiobe index.

Why is Swift losing steam? Tiobe attributes it to developers leaving the Apple-only Swift/Xcode development environment for frameworks that build multiplatform mobile apps such as Microsoft’s Xamarin, Apache Cordova, and Ionic. Xamarin leverages C# while Cordova and Ionic rely on JavaScript.

“Until recently, it was quite common to program Android apps in Java and iOS apps in Swift/Objective-C,” said Paul Jansen, CEO of software quality services vendor Tiobe, which produces the popularity index. “This is quite cumbersome because you have to maintain two code bases that are doing almost the same [thing].”

Multiplatform frameworks get rid of having to maintain two code bases, and they are thus becoming very popular, Jansen said.

In the March 2017 Tiobe index, Swift ranked in 10th place, with a rating of 2.268 percent. But it has been declining since then. This month, Swift was in 16th place, with a rating of 1.668 percent. Not surprisingly, C# and JavaScript are gaining at the expense of Swift and Java.

Jansen does not see a Swift revival coming. Swift’s focus on just Apple’s platforms and developers’ move to multiplatform development all but guarantee a continued decline in Swift’s popularity. “Its growth is over unless Swift is going to be embraced in other areas, which is unlikely at the moment,” Jansen said. The new Swift 4.0 language, which focuses on an improved package manager and compatibility modes, won’t change the situation, he said.

Although there has been discussion about using Swift for Android development, Google is focused on Java, C++, and, just recently, Kotlin, as the languages for building Android apps. So Swift has no obvious place to expand its mobile-focused developer base to.

Tiobe’s index gauges language popularity via a formula that analyzes searches on languages in popular search engines such as Google, Bing, Wikipedia, and Yahoo, including the number of skilled engineers, courses, and third-party vendors pertinent to a language.

Despite falling in the Tiobe assessment, Swift remains ranked 10th in the alternative PyPL Popularity of Programming Language index, which assesses how often language tutorials are searched on in Google. But Swift’s predecessor, Objective-C, beat Swift in the PyPL rankings.

The top 10 languages in the September Tiobe index were:

Java, at 12.431 percent C, at 8.374 percent C++, at 5.007 percent C# at 3.858 percent Python, at 3.803 percent JavaScript, at 3.01 percent PHP, at 2.079 percent Visual Basic .Net, at 2.735 percent Assembly, at 2.374 percent Ruby, at 2.324 percent

In the September PyPL index, the top 10 were: