These may be the preferred languages for these platforms, but at the end of the day, mobile phones and web browsers are computing platforms, and with a little work, you can use any language you want. With the BeeWare suite of libraries and bridges, you can use just Python. And, you can use the same code to deploy on all these platforms.
Python is one of the easier languages to pick up, and it doesn't have the learning curve of Java or Objective C. And recently, many scientific communities, including astronomy and data science, have picked up Python as their go-to language. To be able to use a language they already know to create their own applications, such as mobile-based data recording systems, without having to learn entire new languages would be a great asset to all these scientists.