The problem is that the two molecules nature settled on for photosynthesis absorb only in the far red and far blue, as far as possible, in the visible region, from the peak of solar output. The only living things that can do photosynthesis without green plant forms of chlorophyll are the so-called purple bacteria, which as you can guess from their name, reflect only on the fringes of the visible region, and absorb the peak part of solar energy. But their synthesis is nevertheless not very efficient, and is found only in these single-celled organisms. Molecules have an inherent region of specific absorption, depending on their structure. Molecules can't "evolve," and so once nature settles on a working system, depending on a specific molecule, no matter how imperfect the result, it is stuck with it from then on.

The forms of chlorophyll that make green plant life possible evolved as a key part of a very elaborate molecular factory of interdependent systems--- for cracking apart water and CO₂ molecules, emitting free oxygen as a useless waste product, and transporting bare protons and newly formed complex molecules that act as catalysts for various vital chemical reactions, which eventually produce molecules that are convenient sources of potential energy to power many complex processes!  The most important being the making of more cellulose, in other words more plant.  The very large molecules involved in the first steps can absorb photons only at opposite ends of the visible region.  Once a system this complex evolves, there is no going back, no matter how poorly matched the system is to the actual environment.