this is the general answer. Why is congress punting the "lawmaking" bureaucracy to the executive instead of it being under its own branch.

There are 2 possible reasons I see.

1) having to change the political leadership of it every 2 years (instead of 4) means it possibly wont be as effective.

2) as there is both a "lawmaking" and "enforcement" aspect to it, it makes sense for it to be under "one roof" so to speak, and it would probably be more problematic for the executive to cede that to congress than vice versa.

perhaps there are other reasons? and one can counter the above reasons?