Is that every unit is based on every other unit, no matter how little sense it makes.
Metric pressure is measured in something like micro dynes per fortnight meter lumens or somesuch, (ok, it's really in Pascals or Kilopascals) and no one had a good feel for how much pressure, say 1 million pascals was.
But, lo and behold, 100 KiloPascals (kPa) was just about the same as atmospheric pressure, and atmospheric pressure everyone had a good feel for, so they created a new unit, BAR. Not quite 1ATM, but close.
Actually most marketing information appears to use the conversion that 1 BAR = 15psi (which is why valves on a 3000 psi cylinder are thought of as a 200 BAR valves) to make the answers even more wrong!
Roak
Ps. What about 1 million pascals? Well that's 10 BAR, and you probably have a good feel for 10 BAR, like "about" 330 feet deep (not including atmospheric pressure)!