In nature there are often many different ways to accomplish the same thing. So flowering plants reproduce using flowers, but there are many kinds of nonflowering plants that reproduce in other ways.

Many of the gymnosperms reproduce using male and female cones.
Mosses, liverworts, and ferns have sporophyte generations that reproduce with spores and gametophyte generations that make eggs and swimming sperms.

There are many successful answers to the problem of reproduction.