The market for people who bought 13" MBP was college kids or adults, "pro-sumers" who didn't want an air. Few of them need more than 8GB of memory, but the additional battery life, storage, HDMI, SD, display support, speakers and XDR display make the base 14" M3 worth the extra few hundred to them over the air.

The M3 Pro is the base for actual "professional" users.