People want to sell information and make money but withholding the blueprint that prints. It's like giving you a bit of the cake, while taking away the proper cake from you.

Is it wrong? Absolutely
Is it strategic? Totally

Why try to sell it, if of course you don't want to give it all out

This👇 answers the question

attention is difficult to sustain and you need to constantly give information to stay relevant

Some of them will give you all the information alright, they'll just stretch it out unnecessarily, small chunks at a time. Small enough that you'll get something, but also just enough that you'll need to come back or keep coming back.