[rpedela]

If the question is historical, it is because Python is easy to learn, easy to read, interfacing with C/C++ is easy to get existing ML/DS code, and it was one of the first scripting languages to handle huge numbers which is important in science.

If the question is about now, Python has lots of libraries to help in addition to the previously mentioned reasons. However Java still has better library support for NLP overall such as OpenNLP, Stanford CoreNLP, etc. NLP in Python is catching up though thanks to gensim, spacy, etc.