Adiyen will try to answer this question with whatever kinchit information that adiyen knows.
Lord Krishna in Bhagavad Gita 2nd chapter, Shloka 45 says,
“traigunya-visaya veda nistraigunyo bhavarjuna” : Arjuna, Vedas deal with all 3 modes ( Saattvic, Rajasic and Tamasic ), but you should pick only the Saattvic portions and ignore the other two.
Puranas also are classified in to the 3 types as mentioned above. Veda Vyasa’s role was to share the puranas to all kinds of people. If he had shared only the Sattvic puranas, not everyone will be able to understand the para brahman directly.
Firstly, people need to believe in Sastras and thats the exact reason why we have certain karmas like putra kameshti yagam ( to beget son ), vayavya yagam ( to accumulate wealth ) etc. so for someone who does not believe in sastras, these are the first steps. he performs these karmas , gets the results and starts believing in sastras. slowly, he will progress and finally will get to know that all others except attaining moksha are temporary and surrender to Bhagavan.
Veda Vyasa who wrote all the 18 puranas also mentioned about classification of puranas where he says , ” to aattain moksha, one must catch hold of only saatvic puranas”.
It is the same Veda Vyasa who says,
“Aalodya sarva-saastraani vicharya cha punah punah
Idam ekam sunishpannam Dhyeyo Narayano Sada”
“Satyam Satyam punah Satyam Uddhrtya bhujam uchayate
Vedaat Sastram Param naasti na divam Kesavaat param”
“Raising up my arms, I declare on oath that there is no scriptural text greater than the Veda, and
no deity superior to Kesava. Again and again, this true, is true, is true.”
Adiyen has tried to answer to the best of my knowledge. Request any fault found to be ignored.