Pex has been around for a long time, but it didn't become available in volume until about 50-years ago.
The first PEX material was prepared in the 1930s, by irradiating the extruded tube with an electron beam. The electron beam processing method was made feasible in the 1970s, but was still expensive. In the 1960s, Engel cross-linking was developed.
Pex was brought to the USA in the mid-80's primarily for use in hydronic heating systems. It wasn't until the early 2000's that it started to be used for potable water in the USA.
In 1972, Wirsbo, using Engle's cross-linking method started to supply tubing in Europe. It took about 10-years before it made it to the USA. Wirsbo (Uphonor) is the only company that has a vertical production system meaning that they make their own raw stock. Everyone else buys their raw stock from some other supplier, so don't have as much control over the whole process. That also means that Uphonor has few excuses if there's a problem with their product.