Because in reality they are just sweat shop owners. "Fill in your time sheets" is just a more sophisticated version of "kamar nahi todega toh kaahe paisa dun tereko"
Simple.Because they are rich and get away with it.You by qualification a lawyer, maybe from top law school.But hai toh tu naukar aur woh master.Tujhe uske law firm ke brand aur salary ki zaroorat hai.Usko there jaise 100 mil jayenge.Ge calls the shots.Take it or leave.
Because there are no foreign law firms in India.Once foreign law firms come, all this crassy and cheap behaviour will automatically stop when they will be begging lawyers to join their firms.
Pay you good money (even as a fresher)
Give you a comfortable office with 247 air conditioning, snacks and cab.
Professionally manage thier firms- with opportunity for growth.
Predictability in salary.
On the other hand, senior advocates who make 10* times more money,
Pay you shit - lesser than minimum wages.
Treat you like shit.
Won't give you any amenities or office facilities. And make you work as much as a law firm does.
Will try to pull you down - thier own offsprings will get all opportunities with none for you.
Sometimes won't pay you a buck.
Even some big names in India are like this.