You didnt mention age. My cucs are showing the same. I think patience is the key.

They are self fertile but do require bees to move pollen from the male to female flowers. I find the bees don't work my plants until they are covered with blossoms. So right now I'm doing the pollen transfer with a small brush. The best time is when the blossoms first open in morning. This is about 30-60 minutes after sun hits the plants. It works best on a still, warm, humid morning. You need to cover the brush with pollen and dab it on the females. Expect 20-50% takes at best.

Remember that most vines like those set a ton of male flowers first and those of course can't become a fruit....the female flowers start a couple weeks after you start seeing the male flowers.

Yes, many squash and melon plants start out with all-male blossoms; look for the little miniature fruits behind the flower buds, those are the females, then start the brushing if necessary.