Acquisition Program is not being assigned when a new lead is created by filling out a form associated with a program. The form is embedded in a non-Marketo page.
In order for a program to be assigned as the acquisition program, the form and landing page both have to be child assets of the program. If the form is embedded on an external page, so Marketo has no way to associate the form fill out with that specific program.
You can either use a trigger campaign that looks for the form fill out and assigns the Acquisition Program through a Data Value Change flow step, or put the form on a Marketo landing page within the program.