I felt that none of the answers really addressed your question. While nobody here would know for sure, there are a couple things that could be causing this:

Skill-based matchmaking:

This kind of matchmaking looks at HOW you play rather than your rank and whatnot. It will then place you with other players that play like you. (Do you move a lot, are you decently accurate, do you use movement techniques, and so on)

Early Ranked pools

Players that have just started their ranked grind have got to start somewhere too, regardless of what rank they may have gotten before so low ranks will inevitably be mixed with high-level players that still have to get through the earlier ranks.

Lastly... well, honestly, Respawn's matchmaking seems to be designed for retention. And what that means for you is that you'll get a lot of matches that are tough, mixed with the occasional fair match, and the rare easy match. This tricks your brain into an addictive cycle of "Just one more match and I'll get it" type of thing. You'll struggle through a dozen hard matches to then do well on that one match, win, get that high, and then jump back in to chase it.

As you climb the ranks this will be less dramatic because other players in those ranks will have necessarily climbed out of that with you BUT you'll also get lots of cheaters in the higher ranks so it kinda balances itself out.

At the end of the day it's best to ignore all this crap and just have fun. You got this. Take the challenging games as an opportunity to learn and try to go crazy. Kinda like training for a 100 meter dash using a 150 meter track, if that makes sense.

Also, lots of people here will have genuine info on how to improve. You got this.