Why do few tourists go to the best beach parks in Hawaii for swimming?

Four beach parks are strung like pearls along the outer shores of Hilo Bay on the Big Island, each with clear water, abundant sea life, breakwaters that make for safe swimming, and exquistely landscaped parks and picnic tables along the backshore.  In the distance, Mauna Loa and Mauna Kea rise toward heaven. Okay, so why are tourists absent for the most part?

Answer One: Because it’s Hilo. Indeed, it rains like crazy here, so catching the right day to enjoy fun in the sun is not a gimme. Answer Two: Because it’s Hilo. Most visitors stay in Kona or South Kohala, and when making a trip to the east side they are headed for Hilo Town, Puna, or Hawaii Volcanoes National Park—all worthy destinations that eat up days.
If you head this way on the Big Island, do yourself a favor and make space for a side trip. All the parks are within five miles from main highway junction in Hilo. First up is Onekahakaha Beach Park (first pic above), favored by families who love the picnic pavilions and huge man-made swimming oval. A mile down the road is Carlsmith Beach Park (second pic above). Stairs provide entry into another protected swimming area, a fave among sea turtles. This park comes with a bonus walk into lush pandanus groves at the Lokoaka Wildnerness Park. 
Not far from Carlsmith are two winners sitting side by side, Leleiwi Beach Park and Richardson’s Ocean Park, connected by lagoons and gardens, pictured above. The BBQ’s are smokin’ on weekends at Leleiwa, while surfers flock to the outer break at Richardson’s. Historic buildings add to the charm.
Hawaii the Big Island Trailblazer (pages 152 to 156) has more details on this remarkable coastline, including swimming ponds, a hidden beach, and a totally wild park at the end of the road, just past Richardson’s.