Why doesn't God do something about evil?
The existence of evil is not the result of God not being active in combating the problem. To extinguish evil from the earth, He would have to completely destroy mankind. A spiritual battle exists in this world between God (good) and Satan, the devil (evil) but after the Second Coming, the devil will be cast into the lake of fire. The Lord has given us all free will, and it is up to each person individually to choose between Him and Satan. If the human race were to stop disobeying God's commandments, there would be no evil.
God has provided a long-term solution to the problem of evil. He created hell and the lake of fire for all those who reject Him and blatantly practice sin. He sent His Son to die so that people could be cleansed of their evil ways.
"For the love of Christ constraineth us; because we thus judge, that if one died for all, then were all dead: And that he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again" (2 Corinthians 5:14-15).