Another question along those lines: the Earth is huge compared to primordial life so why didn’t different combinations of base pairs evolve into different types of RNA and then DNA and then animals with different DNA?
Your question contains implicit assumptions which are incorrect!
(This is like asking, "If John Booth assassinated President Franklin D. Roosevelt in 1789, why didn't his Vice President, Thomas E. Dewey, immediately ascend to the presidency? That makes no sense!")
How do you know that different forms of organisms with different kinds of RNA and DNA didn't arise?
There were undoubtedly many different precursor organisms in the Dawn of Life. However, one form eventually hit upon the "right" metabolic mechanism - and then immediately proceeded to outbreed all of its competitors, denying them nutrients and Lebensraum, producing noxious metabolic byproducts that were poisonous to other life forms (see "The Great Oxygen Catastrophe" of 2.5 billion years ago!), if not outright PREYING upon them.
This is akin to the hoary old objection: "If Man evolved from Apes - How come there are still Apes!"
These - and similar naïve "objections" - were first posed more than half a century ago - and promptly answered more than half a century ago.
Regards,