The above happens due to the following:
(1)Soft and sympathetic attitude of judges, jail authorities, politicians, public, media, intellectual class people, etc towards the criminals, wrongdoers, kidnappers, rapists, swindlers, corrupts, acid-attacker guys, etc
(2)Lack of system to keep the culprits under harsh imprisonment for long period of time –jails are overcrowded, lacks sufficient police and jail staff ---so jail authorities seek opportunity to release the prisoners as early as possible to reduce their loads
(3)Lack of system for separate and sequential (one imprisonment starts after completion of the earlier) imprisonment ---criminals laugh at law that they would get same period of jail for one crime, two crime or even over twenty crimes –as IPC has a stupid provision that all punishment would run in parallel ---in USA criminals are awarded multiplied punishments –that is if one murder attracts 20 years imprisonment then 3 murders would attract 60 years of imprisonment –the prisoner would practically remain inside the jail for whole life.
(4)No provision for imprisonment till death, criminals being able to arrange luxurious facilities inside jail, get released early on the ground of GOOD CONDUCT in jail, no fear of death penalty, no fear of extra harsh punishment on escaping from jail or police custody, etc are cause of criminals not hesitating in committing heinous and terrible crimes that would make you aghast and appalled.
(5)Judges hesitate to sentence harsh punishment --because --- some of them are irresponsible or weak-hearten people --- they don’t want to do hard homework for awarding punishment –they simply think “I have no personal enmity with the accused –he has done no personal harm to me or my family or friends ---I am also a dishonest person ---I also do wrong and illegal very often--if I give him harsh punishment then it would be unjustified and may be sin –I may be questioned or criticized --so it is better and safer to sentence light punishment to avoid unwanted problem and fear of sin”. Such judges encourage criminals by giving him/her softer punishment.
(6)Judges may be biased on ground of caste, political link, language, religion, etc. He would tend to give minimum punishment to the person belonging to his own caste or cousin castes, his own political group, etc
(7)Court decisions are often influenced by the power of money, political link, caste, etc.

Pls don't blame police --they have to work under huge constraint, pressure and risk---they are killed by criminals and naxalites and no one bothers ----most time they are not allowed to work freely -- if they encounter such goons, wicked and scoundrels then enquiry is set up, police officers and jawans of the encounter team are suspended, and sent to jail---if they try to prosecute the criminal in the court then judges would release him saying lack of evidences ---if the lower court would give harsh punishment then high-court and supreme court judges would show extra wisdom and mercy to reduce the punishment drastically ---the criminal is sentenced to jail for minimum possible period by the supreme court---after that the criminal enjoys maximum possible luxury inside jail using the power of money, muscle, caste, political nexus, threatening or bribing jail authorities and co-prisoners---he would be able to get the certificate of GOOD CONDUCT by the jail authorities and the Governor and the CM or the cabinet of the state would never bother in acting irresponsibly and releasing him early from jail on the basis of GOOD CONDUCT before the prescribed (already reduced) period set by supreme court ---no one bothers --even media does not raise such issues as why criminals are released frequently before time on the nonsense and illogical ground of GOOD CONDUCT --this is a stupid system and mockery of justice. Any sort of good conduct of the prisoner does not lessen the gravity of the offense and crime committed by the culprit and his good conduct cannot lessen the pain and plight of the victim ---so why to release him on that ground ---this is foolish, stupid, nonsense and bogus system of justice ---it encourages crime –it boost and motivates the criminal as they are sure to get softer and reduced punishment and enjoy luxury even inside the jail ---and get released early---this system needs immediate amendment –that in no case any prisoner can be released early ---but how to stop them from arranging mobile phones, television and radio sets, delicious food, intoxicated materials, and even ladies in many cases for s*xual enjoyment. Prisoners also come out of jail illegally, enjoy some days out side and go back to jail ---they often get admitted to hospital on completely false ground of illness and enjoy more freedom and luxury in the hospital ---corrupt jail authorities help them in all these activities.