You don't get why people would like to be in control of a powerful new technology before they build their stuff arround it ?

Sure, there might be currently contraints, but I think it is quite possible training will get optimized over time or crowsourced training can be organized.

Without fully end-to-end open source models you are still at the mercy of the model provider to keep providing updates, you have no idea what garbage they trained the model on & can't fix that, not to mention might end up getting sued for using the open weigth model once all those "AI stole my data" lawsuits are finally decided.