Motorcycles

So a few reasons:

Hawaii has a non-mainland, dont-look-like-you're-trying-too-hard kind of vibe. Business people don't wear full suits downtown. You're not even supposed to show up at the interview in a suit or you'll look off. Unfortunately this crosses over into motorcycle safety. So if you ride all geared up, you'll look like you're...not from Hawaii.

Island infrastructure is also pretty delicate. Traffic can be frequently gridlock and unpredictable. There's been a few cases where a traffic incident shut the entire island down for most of the day. Add that it's hot most of the year and you get tank top riders.

Most island residents, probably most of the ones you see riding, don't have high incomes and Hawaii is one of the most expensive states to live in. Gear is expensive. And they got that bike from their cousin.

Source: From Hawaii and rode there too.