Why doesn’t God prove His existence?

Do you think everyone who is thoroughly convinced God exists always does the moral thing?

Seems to me it is obvious 'knowing' that God exists doesn't keep people from doing evil.  Best I can tell from the OT, the Israelites were often instructed to slaughter other people....down to the women and children and livestock.  And even if they didn't actually DO any of the things they wrote that their God wanted them to do...writing it down was evil because I think it led to lots of other atrocities throughout history. Was what they were told to do moral or were they simply wrong in their interpretation of what God wanted them to do.  The Jews in Jesus' time seemed hellbent on having Jesus executed for his blasphemy yet they also seem totally convinced God existed.  Best I can tell, the RCC throughout the middle ages did horrible things all the while genuflecting and groveling before the Christian God.  As I understand it, Hitler was not an atheist and still committed horrendous act slaughtering millions.  Some extremist Muslims commit horrible acts of terror all the while totally and unequivocally convinced God exists. People's for millennia kept/traded in slaves yet by and large ALL OF THEM knew God existed.  Even today, we see evidence of deeply religious and theistically convinced individuals doing what most much of the rest of society sees as immoral.

But more importantly, I just don't get why a world without sin, because everyone was absolutely convinced God exists and was absolutely sure exactly what God wanted them to do, is so bad. There is a lot of latitude in what one can do while only doing good and never committing heinous violent crimes or lying cheating or stealing. One can live their lives out with lots of flexibility and variation of only moral things to do.  In fact I would guess that for most people, most of their decisions...important beneficial decisions don't involve a choice between right and wrong at all.  Do you see every decision you make in your daily life always and absolutely a moral decision?