Product page is the one context with access to Trigger rules — targeting by the specific product or collection being viewed — because it's the only surface where "the page itself" is a meaningful targeting signal; every other context targets cart or customer state instead. That makes it the natural home for pairing-style offers ("viewing X, suggest Y") that wouldn't make sense once a shopper has moved on to the cart.
Otherwise, product page sits at the top of the capability range: all five behavior modes, full layout options including carousels, and arbitrary hex-color styling, since it renders through your theme rather than through a Shopify-controlled checkout surface. If an offer needs a capability that another context lacks, product page is usually where it's available.