Calling a PRNG is way easier than any of the alternatives. Coordinating sequences on a bunch of nodes so that nobody overlaps is a pain in the ass, and a point of failure. Incorporating some notion of "machine ID" in the identifier makes it easier, but you still have to worry about multiple pieces of software on the same machine, for example. UUIDs are the a good solution, but you need a UUID library you trust, and they waste a lot of space / are overkill for many use cases.

All of that is sort of beside the point though. Pseudo-random sequences are useful for lots of things and the PRNG algorithm behind Math.random() is pretty crappy.