Drive train losses. Turbo charging is slightly more efficient.
Supercharging was used because the response time was better, less lag which was more noticeable in a petrol car versus a diesel due to the torque gap at low revs. Now with ball bearing turbos, variable vane, sequential turbocharging and electrical assistance, lag is almost gone - so now turbo charging is being used much more than before.
Sent from my Pixel XL using Tapatalk