Adam was gifted with a System called 'God's User Interface (G.U.I.)' by 'God' after his original life had ended. The reason? 'God' had seen the increasing number of isekai stories throughout the world and the public at large seems to have been drawn to this idea with many praying for the chance to be in that sort of situation.
As such 'God' wanted to give the world this chance but he wanted to have a trial run first with one person to see if it would work without completely breaking the natural order of the world.