Power politics.
Russia is reluctant to grant Chechnya independence for geopolitical and economic reasons. For one, the country has important natural resources - oil deposits, natural gas, and various other minerals. Also, an important oil pipeline runs through Chechnya from the Caspian Sea. Besides, Russia is an extremely vast country, so if Chechnya were allowed to break away from Russia, plenty of other territories would be demanding independence as well, even more loudly than they are now.