I think you are slowly drifting from the position you started from. You used word rejected without any good reason then you said people strayed hence need for NEW religion.
You hve not read my above post carefully.
I asked why would same Allah reject his own teachings?
With Islam coming in to Arabia, the previous ‘religions’ were not condemened or rejected my friend.
I used word religion for simplicity but technically Judaism/Christianity and Islam are extension of SAME religion with modiifcaton/improvement.
As for your question, I already mentioned yes previous ‘methods’ were to be abandoned but basics were not rejected.
Quran is full of good words for prior prophets and their teachings. So how come a muslim can say Judaism or Christianity were REJECTED?
All muslims believe and you also mentioned that other scriptures were adultrated/changed and hence no pure teachngs of previous prophets are left ( some basics may still be same though), hence, no one now truely follows pevious teachngs and when improvised verson is available and is emphasized (as per islamic teachings) then this improvised version need to be followed.