I've thus far avoided using it, but my recollection is that it kinda snuck into mainstream stacks because it was part of the standard deployment model for the ~

I've thus far avoided using it, but my recollection is that it kinda snuck into mainstream stacks because it was part of the standard deployment model for the ~2015 era of "big data," with Hadoop, HBase, Solr, and the other usual suspects from the Apache Java ecosystem. Nobody chose to have Zookeeper in their stack, but they needed it for these other services and so eventually they were stuck with it.