Can’t really blame them, since most of them never experienced the results of conscious manifestation… and if you never try, you can never succeed.
The conundrum here is that you have to believe it can be done for it to succeed—which means if you’re not a believer from the get-go, you probably won’t see results, and then you won’t become a believer, and so forth, ad infinitum.
And if these people did, by chance, manifest something out of the realm of the ordinary, they are just as likely to explain it away as “coincidence.” Granted, a monumental coincidence, but still.
I usually tell people to start with something small—just because our mind is more willing to believe that you could manifest something small, like a feather, even though there’s really not much difference between that feather and, say, a new refrigerator.
But as always, perception is everything.