Actually, I'll honorable mention Ken as well.
Reason #1? Ken is awesome
Reason #2? As kids, when we played World Warrior on Super Nintendo, my brother always insisted on taking Player 1, and immediately picking Ryu. So I had no choice but to pick Ken. And I grew to like Ken as a character a lot, he's a consistent main for me across all Street Fighter games. (Same reason I grew to like Luigi as well, my brother would always take Player 1 and therefore, Mario. So I had no choice but to pick Luigi.)