My five word explanation why the Germans lost in the east.
"Russia is too damn big."
Partially. But it also has a lot to do with Nazi ideology in combination with the arrogance of German leaders.
Germany wanted too much out of the war.
a) Eradication of Bolshevism/Marxism which is seen as one of the two primary threats to Germany and western Europe (the other being Jewry).
b) Living space which would be confiscated from Slavs and given to German settlers in the post-war.
c) relocation or extermination of Slavic peoples.
The only realistic (and perhaps moral) goal would have been a); to topple the Soviet regime, install a nationalist fascist/pro-German government that would make some generous concessions to Germany in the post-war and otherwise act as a puppet.
Germany would have had to galvanize nationalists in the USSR, promote national/religious groups that naturally oppose Bolshevism and become their champion.
Instead Nazi Germany saw themselves as a conquerer and master, not a liberator and ally. Of course it couldn't have been any other way as it is really hard to divorce the racial-bigotry from the rest of the Nazi mandate.
Nevertheless had Germans been less racially focused and more interested in securing Europe from Bolshevism as they claimed then it would not have been impossible to win the war by toppling the Soviet government.