A retrospective. The short answer is basically that MATLAB changed their licensing to exclude the Fraunhofer Institutes (possibly unintentionally), and Fraunhofer people responded by rolling their own.
Interesting point made: if it takes minutes to load up your dataset, it's nice to be able to work with the heap in a dynamic manner, adding new functions to work with the data structures already in memory. Python has ways of making that easy, and of course MATLAB had that rolled in from the start. Any REPL language can do that.
This is essentially a question of in-memory indexing of a database.