"A common misconception is that transactional confidence is based on time"
Transactional confidence is based on the probability of someone compromising the network for enough blocks to undo a spend that you've already honored (IE you gave them what they paid for, then they undo the transaction). At 6 blocks, you are assuming that an attacker won't have the computational power to reverse 6 blocks in a row.
When blocks come out every 2 hours, that means you need to find every single block for 12 hours, or essentially control the blockchain for a long time.
When the block rate is down at 5 minutes, you only need to control the network for 30 minutes - you have more chances to get lucky and undo 6 transactions in a row in your 12 hours of purchased computing time.
A halved block rate does not mean you need less computational power, but it does mean that computational power is probably cheaper and 6 blocks worth of power is going to be more affordable.
Transactional confidence is based on the probability of someone compromising the network for enough blocks to undo a spend that you've already honored (IE you gave them what they paid for, then they undo the transaction). At 6 blocks, you are assuming that an attacker won't have the computational power to reverse 6 blocks in a row.
When blocks come out every 2 hours, that means you need to find every single block for 12 hours, or essentially control the blockchain for a long time.
When the block rate is down at 5 minutes, you only need to control the network for 30 minutes - you have more chances to get lucky and undo 6 transactions in a row in your 12 hours of purchased computing time.
A halved block rate does not mean you need less computational power, but it does mean that computational power is probably cheaper and 6 blocks worth of power is going to be more affordable.