I strongly suspect a lot of the huge tech companies don't actually know why they do things. There isn't a grand plan. There's a vague notion of "It'd be cool if we had a source for data for X, Y, and Z, because then we might be able to do A, B, and C!" They then build the infra for gathering the data, find that A, B, and C are actually harder or less valuable than they figured, and just carry on sucking up the data in case they dream up a use for it in the future.

There are examples of this happening. Niantec built Pokemon Go, made a lot of money from, sold to the Saudi Wealth Fund for even more money, and then the company pivoted to selling all the map data for telling delivery robots where your front door is. I don't think that was ever the plan when Niantec were storing all that data to optimize where to put a Magikarp. it just happened that way.

Isn't it some kind of Asimov's Foundation thing? You track to be able to predict. The better you predict the more power you have.

if they don't track human then who they gone track ? humans use their product so why they should not track it, but they are going out of the line by tracking personal things and using them for ads or any advantage, and we are so much reliable on these products can't do anything

So they have the ability to track people who object to their dominance. The first category of work any surveillance technology is put to is surveilling those who publicly don't like that technology.

In my opinion, it's so they can track consumer's habits so they can market more stuff to you. They also do it so they can sell the data they collect on you to other companies who want the same thing. Round and round we go, until all of Silicon Valley knows what you buy, browse, and are likely to want.

But maybe that's just me being cynical.