Pressurized explosive gases are dangerous. Your propane task isn't part of a multi-ton vehicle traveling at high speeds that may be subject to a high speed crash at any random point in time.

A hydrogen tank that is part of your car, however, may be subject to a high speed crash coming in at a random angle.

BBQ grill propane tanks can explode, but they are typically stored on porches, an environment where they are not often hit by SUVs.