Why can't I spawn with the more powerful weapons in matchmaking?

I wanted to play Gears of War 4 multiplayer. But, for some reason, when I was going into spawn, my load out could only handle the lancer, gnasher, snub, hammerbust, and the enforcer. Why can't I spawn in with the more powerful weapons like a sniper or torque bow?

In matchmaking, the default weapons are those that you stated (Gnasher, Snub, Hammerburst, Enforcer, Lancer). You can select only between those weapons as your load out guns.

The other weapons you mention (Torque Bow, Sniper, Boomshot, etc.), must be found on the map you are playing on. I believe if you hold one of the bumpers (I think the left one), it will highlight on your HUD where you can find the more powerful weapons. However, you will have to get to them quick, as the other players will likely try to get them as well.

Note that the guns rotate in and out of play depending on a few factors (the map you are on, the game type you are playing, etc.). In Horde mode, depending on what class you are playing as, you can start with some of the more powerful weapons, like the Sniper and Boomshot.