Nerfing of cards

I have a question for anyone who else finds this interesting. Why does Blizzard nerf the overpowering cards but doesn’t do anything about all the cards that rarely or never see play? Wouldn’t “bumping up” lesser played cards diversify the meta somehow? If more cards were viable, it seems to me that we would see more deck variations in standard and we wouldn’t always see many players using net decks in ladder. Thoughts?