Odin replaces Thor with Fred Norvell because Odin resents Thor training High Evolutionary’s New Gods.
Odin is a dick who provides the exact opposite of unconditional love.
No wonder Thor has such extreme daddy issues.
After fighting and yelling, Odin tells Thor bits of his history that we’ve never seen before. For example, he tells Thor that while his body and Don Blake’s were tied together, Blake’s body would go to Wundagore mountain while Thor was running around–and Thor would disappear while Blake was around. Odin said he did this to avoid Ragnarok–thinking that a prophecy involving Thor wouldn’t happen if Thor was nowhere to be found.
In the end, Odin asks Thor to stay in Asgard because there’s a new Ragnarok coming, but Norvell will also be there so Thor says no and returns to Earth.