There were similar connector standards that preceded 38999, e.g. MIL-DTL-5015 as far back as the 30's, which evolved into a couple of subsequent standards, with 38999 emerging in the 70's.

Edit: just realized you were maybe referring to the LEMO F-Series compatible connectors. Sometimes a company just designs a new connector. The F-series stuff gets used on stuff like instrumentation that may or may not be ingress protected, and has a need for extremely small size and potentially getting mated/unmated often in service. My assumption is that LEMO found that there wasn't a connector on the market that did this well, and spun up a niche.