But can’t carry much

Skill issue. I've seen washing machine+dryer+refrigerator on the back of a 125cc quite a few times, and I'm comfortable riding at highway speeds with 2 checked-bag size suitcases in my side racks and a backpack and carry-on suitcase behind me.

4 people in a hybrid use far less fuel.

4 people on 1 bike uses less fuel than 4 people in a hybrid, its extremely common here in SEA.

But if most of your trips involve transporting 2 or more passengers, then bikes aren't so attractive.

You're probably looking at a 125cc that takes 20 seconds to get up to highway speeds.