The rewards for Bitcoin mining are reduced by half roughly every four years.When bitcoin was first mined in 2009, mining one block would earn you 50 BTC. In 2012, this was halved to 25 BTC. By 2016, this was halved again to 12.5 BTC.
Pakistan hasn't created any regulation that bans people from mining cryptocurrency.In fact, given that public cryptos are mined using your own computing equipment, it doesn't interfere with any laws at the moment.