The total cost of mining is usually similar to the block rewards.
It is still cheaper than cost of maintaining today's banking system, many many folds.
then why governments are not adopting bitcoin, it would be a win win situation for them, if the cost are vastly cheap, is only regualtion that prevent this? or there is somethign else...
i think they just don't like to not have the control over money
The answer is quite simple, although this might be a little off the topic. They are never going to adopt something that they can not control. If everyone were to use Bitcoin this moment, the banks would start dying out pretty quickly in my opinion. They could only die if someone were to start offering loans in Bitcoin (like banks do).
Actually they are trying to find ways to use the blockchain technology because it is cheaper for them. I wonder how much power banks waste compared to Bitcoin?