I got to visit the control centre while it was under construction back in 2016 (I think: I was one of the guests at an SF convention, hence the special group tour). One factoid that stuck with me was they also considered micro-Python, but Javascript won because it supported floats. They were looking for an embeddable scripting language that astronomers could reasonably be expected to learn or already use for directing observations, so it had to be compact, very popular or ubiquitous, expected to remain so throughout the working life of the telescope, and easy to learn. (It was to be used not by CS grads but by astronomers.)

It's a cut-down subset of the language and bolted down to prevent idiots installing random packages off the internet on an irreplaceable $10Bn instrument.