Here's why Creatards might be right

[Esquilax]

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 .

Because the semi-random genetic mutations that constituted our evolution took us along a different path, supported by an ecological niche that was amenable to our current survival strategies.

and what do you think started this process to begin with ?

Chemicals working in energetically favorable ways in accordance with the laws of physics and chemistry. If you're just going to turn around and ask what started those, then I need to ask you why you think an "I don't know," answer would suddenly be evidence for intelligent design?