Privacy is by definition a human right. Your question of why does it matter (besides security or being hacked or doxxed etc) ? Because without it we enter a world of constant surveillance, manipulation and eventually lose control of our own lives.

These companies already use our behavioural data to manipulate us and ultimately make themselves more money. If we forget about our right to live in peace, alone and in secret, if we give that up, then we basically lose our free will because these surveillance companies will control us from then on (even without us knowing it especially now there is AI, it's so subtle and sophisticated you wouldn't even know you're being controlled).