My understanding is it mostly came down to resources. Everyone leading up to the war was pretty much on the same page as far as theory went. There were a few paths that were the most likely to be successful. But the Germans estimated the cost and the timeline to develop them and thought it wasn't feasible for them, and that they should put there limited resources into other things.

The US was able to work on all the paths and quickly found out that one of the paths was much more viable then the others and then focused on it. When they released information a few days after the Hiroshima bomb to prove that it was an atomic bomb that they dropped on Japan, the release had enough information that Heisenberg and the others then understood the steps to get there.

The BBC has a podcast on the topic. The last episode focuses on the events your question is about. It's not my favorite podcast, but it's not a huge time suck and there is lots of good info in it. https://www.bbc.co.uk/programmes/p08llv8n/episodes/downloads