Probably because the game was designed to reward players for completing challenges over doing well and winning the match.
I’ll still play to win but most times I question why I should when I’ll get more xp for focusing on giving 5 Spartan’s back massages etc. than actually playing well and going for the objective. Wins mean nothing in this unless you have a challenge for it…
True… you get a measly 50XP for completing a match (but it randomly goes up to 300XP at times 
), should get more for a win
Your first completion of the day gets 300xp. After 7 games, it goes to 50xp.
It isn’t random at all.
maybe they want to die i know in streets, Live fire and some maps i toss grenades right into it’s spawn to kill enemies.
Oh, thanks for that. Shows how much I’ve been paying attention 
Wait… so what happens between game 2 and 6?
You get 200, 200, 100, 100, 100.
match 1 = 300 xp
match 2 = 200 xp
match 3 = 200 xp
match 4 = 100 xp
match 5 = 100 xp
match 6 = 100 xp
and after that every match will be 50 xp
So for every first 6 matches per day you will gain a level, since they are a combined 1000 XP