Question

If the current is directly proportional to potential difference, then why the is V=IR not I=VR.....

Answer 1

The physical significance of the quantities V and I is where V defines the potential, i.e the ability to drive the flow of electrons, I measures the actual rate of flow. So, naturally the actual flow depends directly on the ability but is limited by restrictive forces that inhibit the flow of electrons in the conductor. This property of conductor was termed as Resistance.

If it was to be framed as I=VR, or let's call it as I=VK, then the physical significance of the quantity K, would have been the measure of Conductance of the material instead of the Resistance. Now since there was a studied and defined quantity for the restrictiveness of flow electrons called Resistance, instead of introducing the new term as Conductance, they defined it as inverse of Resistannce. So the equation came out as:

I = V * (1/R)

which gets reshaped to V = IR.

But yes, you had a point to make that it should have been more intuitive to put I on the left and V on the right since it is more practical to realise a constant V source than a constant I source.

Hope this helps :)