Here's why Creatards might be right

[TheRocketSurgeon]

but if 'the chemistry for life on this planet allows for it and nothing prevents it'  and thats the reason why it happens then why dont humans use photosynthesis also ? we live on the same planet with the same chemistry . and what do you think started this process to begin with ?

It doesn't mean it's a foregone conclusion.

But to answer your question, the reason is that photosynthesis turned up after life had already diverged into the types of bacteria that would become animals and that which would become plants, on the later earth.

Our ancestors absorbed and formed a symbiotic relationship with a type of Alpha-proteobacteria (sometimes this ancestor is referred to as "purple bacteria"), in which the cells gave it shelter in exchange for its by-product of metabolism, adenosine triphosphate (ATP). From then on, they were transferred as a symbiote, through cell division and later in the egg of each mother down to us-- which is what allows us to trace "Mitochondrial Eve" through the matrilineal inheritance of mtDNA, the separate genome found in our mitochondria.

On the other side, a similar relationship formed between cyanobacteria, a bit like algae, and larger cells, for a similar relationship-- shelter for better food. Descendants of these would become the seaweeds and the plants that would later colonize the surface, though it's the oxygen-producing effect they had in the oceans that led to the rise in O2 and thus O3 (ozone) which blocked enough UV light to allow plants and animals (having evolved separately, in the oceans) to both colonize the land.