Imo, Tryndamere is not so good in low elo, and for a few reasons.

Hes very unforgiving. One mistake, you get behind, you cant beat the other toplaner in 1v1 anymore, you're now useless. You dont have any cc/utility, unlike a Tresh for example and you wont get back into the game the same way a Yone or a Kata could.

He's a splitpusher and arguably has the worst teamfight of any champions in the game. People dont know how to play around splitpush in low and will more than often spamping you and tilt because you werent there. Low elo is a lot more "Aram" than high elo, and Tryndamere performs really poorly in those.

You need to positionne yourself well. One good Lux cage, you get burst, you need to R to survive and back off immediatly and you're now useless for 80s. People in low elo dont positionne themselves well. You also "only" have 5s invincibility, and you need to positionne yourself well to be able to use them effectively.