Hence why...

[Primrose123]

Is it incorrect to say 'hence why'?

I've heard and read it quite a bit lately, and it just sounds wrong, but I don't know why. Is there a rule when using 'hence'?

Sounds wrong to me...

In that context hence means 'which is why'. So it's like saying 'which is why why'.

I think you should probably use 'hence the reason' instead of 'hence why'. It just sounds better.