Apple claims that the iPad Air (4th generation) has 4 speakers, but only the ones on the left side (top & bottom) work, why is it so?

Apple DOES NOT claim a 4 speaker audio system on the iPad Air 4.

Apple states that the 2020 iPad Air 4 has a true stereo speaker system which uses the top left and right speaker ports,

The 2 lower left/right speaker ports are just there to act as additional sound resonance ports to help amplify the iPad Air's sound levels.