> The same language, rituals, stories, music, food, imagery used, are all pretty much alive outside and inside thousands of temple even today.
Technically, it's not the same language, culture, etc. The living culture has changed considerably over the centuries both organically and via outside influences, including Islam.
The surprising thing about India is that it has kept around so much of the really ancient stuff while also adding a huge amount of new stuff along the way. Cultural hoarding, if you will.
It's like the cultural change process is sedimentary, with previous layers being preserved below, while the newer layers get added above, giving a kind of continuity, whereas in other parts of the world, it has often tended to be a more volcanic process, with the destruction of what preceded.
Also, Indian culture long ago accepted what to Western thinking seems like a contradiction of polytheistic icon based religious worship and the belief in a more abstract deity, or even atheism.
In the West, this resulted in the complete disposal of the previous pantheons, but in India, it was rationalized through a "many perspectives" lens where all the viewpoints could be accommodated.