Why do my variable product cards say Select Options instead of Add to Cart?

This is on purpose. A Variable product can't go into the cart until the shopper picks a size, colour or other option, and a product card has no room for that. So on every product box design, Wcart changes the card's cart button to Select Options. Clicking it opens the product page, where the shopper picks the variant and adds it to the cart.

Subscription products get Choose Plan for the same reason.

To make it quicker for shoppers:

• Hovering the variants badge on the card lists up to five options with prices. Clicking one opens the product with it already picked.
• Simple products keep their normal Add to Cart button on the card.