Why maturity rule on coinbase tx requires too many confirmations w.r.t an arbitrary tx? For an arbitrary tx, it is often said that 6 confirmations is sufficient. However, maturity rule states that coinbase tx can't be spent until it receives 101 confirmations. Why do we have this disperancy? 

Why 6 confirmations on coinbase transaction is not considered as sufficient for example ?
If a normal tx is honest, has 6 confirmations, and there happens to be a reorg 6 blocks deep, the tx will just go back to the floating pool, and join one of the next blocks, with no harm done to any party.

If a coinbase tx has only 6 confirmations and there is a reorg, the original coins vanish from existence, invalidating the transaction, and any subsequent transactions that depend on it. These transactions can no longer be accepted into a block, and even if all parties involved are honest and willing to go through the effort of resending, this cannot be done because the original miner no longer has coins to send, and neither do the other parties.

Since a reorg invalidating a coinbase tx is catastrophic, a safety net of 100 blocks is required to make the chance of this happening vanishingly small.