Do you not like a challenge or are shooting games not your thing?
Well, 4 vs. 20 is challenging enough for me. :lol
Personally, if I'm not playing an online game with real people, I like to feel smarter than the average bear. I have nothing against a challenging game against CPU controller players, but ultimately I realize that turning the difficulty up on bots doesn't help me improve my game, or help me to improve my strategies and ability to out-think my opponent, it just means that a CPU bot is gonna get a headshot on me every time I see him, simply because he is a computer and will not miss. To me, that's not fun, that's just frustrating. I can even set up a perfectly good ambush in order to catch the CPU off guard, but being a computer whose AI is tied in directly with every part of the game, there is no "suprising" him at all. Actual tactics and strategies go out the window, and it turns into a game of repetitive strafing battles.
Plus, slaughtering the opponent is fun. I like going into a mutliplayer match knowing I'm going to win one on one battles nearly every time, but I do also enjoy a tactical challenge, so to even things out I add more playres to the other team and ensure that one on one battles happen a lot less frequently.
I guess to me, defeating an opponent by distracting him while a well placed sentry gun does the dirty work is more of an accomplishment than simply lining up my crosshairs on his head quicker. Especially when I know quite well if a CPU bot wanted to he could get a headshot on me quicker every time.