Captain Olimar and Captain Falcon were very different; Falcon was a big, strong, and famed hero; Olimar...not so much. He felt out of place among all the other Brawlers. He was tiny, for one, and his fighting skills were next to none. He wasn't sure why he had even been summoned to help in the Subspace Emmisary, or how his name had even been imentioned/i. He was weak, and so were his Pikmin, as far as he was concerned.
So nothing between them was immediate.
When they met, Olimar was terrified of Falcon. How could he not have been? With a single punch he wiped out an entire army of Pikmin! Olimar had resented him for the longest time because of that. And to top it off, he dragged him right into battle! He didn't seem to care about Olimar's size or strength, or listen to his protests, or notice that he was scared shitless of him. Maybe he had just wanted a companion, or, after saving him from that robot, maybe he felt obligated to protect him. During that time they spent together, Olimar never thought of it like that. All he could think about was how far away he wanted to be from the man. It took a while, but Olimar slowly began to see that Captain Falcon wasn't such a bad guy after all.