>>509805008
>Why would Nazis even need camps to kill all the Jews?
Containment,isolation and slavery for the war machine. The ghetto system was inefficient and lead to situations like pic related. Word spread about what was really happening after all and this lead to uprisings and futile but brave resistance attempts.

>Why the Nazis didn't just kill them all with Gestapo and SS death squads
They tried and the mental toll on the men doing it (lots of suicides, psychosis events and widespread alcoholism) was so enormous that Himmler ordered the gassings first they tried with mobile trucks(using the diesel fumes first),but that was slow and painful and then with methods such as explosives in bunkers and eventually gas chambers after practicing with Zyklon B on prisoners in Block 11 of Auschwitz I.

Around 1.1-1.2mn were killed by death squad executions in massacres across eastern Europe. Babi Yar near Kiev is a famous major one but there are many. I included a colour pic of that location in this thread.