Why Arena 4v4 and not 5v5?

If I remember correctly every Halo multiplayer would have at least one or more 5v5 playlists somewhere, while the more competitive stuff would stay 4v4. I consider myself a casual and competitive player, because while I enjoy casual play most of the time, I really only enjoy it with competitive elements like 100% even starts. I was always for even starts even on the the most crazy casual game types.

Now with that said, I still lack the competitive understanding of why 4v4 is more popular than 5v5 and I’d like someone to kindly explain it to me. How is adding one extra player to each team make it less desirable to play competitively? I see it as one more player to kill and one more teammate to help out.

My educated guess is because it’s what the pro gamers wanted.

And of course, 343 chose to do whatever pro gamers want.