It does but only due to practicality.

Seismologist Susan Hough has suggested that a magnitude 10 quake may represent a very approximate upper limit for what the Earth's tectonic zones are capable of, which would be the result of the largest known continuous belt of faults rupturing together (along the Pacific coast of the Americas).[17] A research at the Tohoku University in Japan found that a magnitude 10 earthquake was theoretically possible if a combined 3,000 kilometres (1,900 mi) of faults from the Japan Trench to the Kuril–Kamchatka Trench ruptured together and moved by 60 metres (200 ft) (or if a similar large-scale rupture occurred elsewhere). Such an earthquake would cause ground motions for up to an hour, with tsunamis hitting shores while the ground is still shaking, and if this kind of earthquake occurred, it would probably be a 1-in-10,000-year event.[18]

So a 10 could be like, if California decides to finally go walkabout. Physically possible, but the sheer amount of movement a part of the crust would need to experience is very unlikely and therefore a scale measuring that or above isn't needed.

But a quake higher than 10 is considered impossible with current conditions, so in practice it does.

You know, unless.