Combination of factors.
1-SBMM systems in “social” playlists make everything, and everyone, play like disgustingly sweaty people.
That environment is not conducive to a Fun experience for 95% of the player base who aren’t psychotics masochists with sever mental hang ups about what “casual” is suppose to mean.
2- The weapon sandbox is bad.
-List of Problems-
Half the Weapon Pool is utterly inferior to the other Half.
You have an extremely high probability of spawning with weapons that will not win you any fights.
There is only one “Real” powerup you ever actually want, and its the Grapple. Everything else pales in comparison, including the Repulsor.
There are at most 5 Viable weapons that you WANT to spawn with. 6-7 if you’re exceptionally good at Snipers.
Rockets, Skewer, Sword, Gravity Hammer, Cinder Shot.
Every other weapon in the Pool rangers from “I can get a couple kills with this,” to "I am someone’s KDA 
"
If what you spawn with something that can’t 1shot the next enemy you see, you’ve been delt a bad random hand.
3- Infinite’s maps are bad in general.
The only exceptional maps are Recharge and Behemoth, since they make interesting use of their scale and their space.
Everything else just does not work, most of them suffer from terrible map flow, and exceptionally abuseable camping spots.