I made my own many years ago from thin utility strapping, the sort of thing people use to attach sleeping bags etc, to rucksacs, with a strong plastic buckle.
A major advantage is security. If the pin pops on a conventional watch strap, the strap is broken and you are quite likely to lose the watch.
With a strap that goes through both pins, the watch remains attached but flaps around so you'll notice you lost the pin.
IF this style was universal, fixed pins could be used, but that isn't likely to happen.