Question

can anyone explain it..

Answer 1

yes it could be if these units be different...
scientifically its possible

Answer 2

On the practical use make it all equal to 1 and then you can write the way you want.

So, if speed=distance/time it means distance traveled per unit time.

And very similarly if we say

speed=time/distance it will mean time taken per unit distance.

Both give us the same understanding but with different references.

If you want to write speed=time/distance go ahead it's just we humans respect our ancestors so we consider what is said by them atleast in scientific formulas.

That's the reason we conventionally right

speed=distance/time.