Creatures on Earth has 2 modes of reproduction, sexual and asexual. Most species employ only one of the two strategies, but a handful use both. Those that engage in sexual reproduction are either monoecious or dioecious. Most on Earth are dioecious (each individual has one type of genitals), but some, like certain worms and snails and plants, are monoecious (each individual has all types of genitals).
Notice how on Earth, "monoecious" is completely synonymous with "hermaphrodite"? On the planet I'm worldbuilding, most of the species engaging in sexual reproduction are monoecious, but not hermaphrodite either. They're all just one gender, producing only one kind of gamete capable of merging with the gametes of all other individuals of their species.
This strategy seems to yield better reproductive success as you can mate with all individuals of your species just like hermaphrodites, and at the same time only produce one type of gamete thus cutting energy costs unlike hermaphrodites who have to produce two types of gametes at the same time.
Is this idea plausible? A whole planet where the vast majority of multicellular organisms living there are monoecious. Why didn't any organisms on Earth ever come up with this configuration for reproduction?