Like many developers, when it came to building data-intensive projects, using Python wasn't my first choice. To be honest, having worked with Java for so many years, Scala seemed much more attractive to me at first, even though the learning curve was pretty steep. Scala is a very powerful language that elegantly combines object-oriented and functional programming, which is sorely lacking in Java (at least until Java 8 started to introduce lambda expressions).
Scala also provides a very concise syntax that translates into fewer lines of code, higher productivity, and ultimately fewer bugs. This comes in very handy, especially when a large part of your work is to manipulate data. Another reason for liking Scala is the better API coverage when using big data frameworks such as Apache Spark, which are themselves written in Scala. There are also plenty of other good reasons to prefer Scala, such as it's a strong typed system and its interoperability with Java, online documentation...