The most common reason, in my experience and in the people I've talked to about this, is that the practice is happening on the surface but the underlying self-concept hasn't shifted.
You can do affirmations, scripting, SATS, the whole stack of techniques, and still get nowhere if at the level beneath all that practice, you actually believe that money is hard for you, that financial ease is for other kinds of people, that wanting more is somehow shameful or unsafe. The techniques skim across the surface of an unchanged assumption, and the assumption is what's running the show.
The work, if you're stuck, isn't to do more techniques. It's to look at what you actually believe.
Try this. Sit down with a notebook and complete these sentences, without editing yourself:
Money in my life tends to...
People who have money are...
If I had a lot of money, I would worry that...
The reason I haven't manifested more money is...
Whatever comes out, that's your operating assumption. You can't shift what you haven't named.
The other major reason people stay stuck is that the nervous system is in chronic threat-response, which means the body is broadcasting a signal of unsafety that no amount of conscious affirmation can override. If you're constantly anxious about money, the affirmation "money flows to me easily" is being said over a body that's screaming the opposite. The body wins.
For that, you need somatic work alongside the manifesting practice. Bessel van der Kolk's research in The Body Keeps the Score makes a strong case for why the body's state has to shift before the cognitive practice can land. Breathwork, regulated movement, practices that signal safety to the nervous system, those have to happen for the manifesting work to penetrate.
If you've been practicing for months and seeing no movement, the question is almost always one of those two things. Self-concept or nervous system. Address either one and things start to shift.