Microscopic lifeforms outsie earth exist thats a fact (bacteria on asteroids etc).
And since creating microscopic life is a way bigger hurdle than evolving this into more complex lifeforms (which just takes time and not the BIG COINCIDENCE/EVENT/WHATEVER YOU WANNA CALL the thing that started all of it)
Its just normal to assume there is life on other planets. That doesnt necessarily have to be able to understand math or speak or whatever but thinking there is no planet with well lets say alien-equivalents of insects or bugs is just ignorant.








