There are more options than those two.
Sometimes things favour different skillsets, If someone lacks the skills required to do something they are unlikely to do it very often if at all.
Just because someone is a higher rank with a particular hero doesn’t mean they are equally good with all heroes or that they have all skillsets at a high level.
Heroes require different levels of positioning where as some can make mistakes and hit their “Whoopsie” button and have that mistake undone and still do well.
If they didn’t have the ability to do that with their preferred hero their rank would be a lot lower.
Other players can brute force their way forward by aiming faster, Reacting faster.
Also worth mentioning is not all high ranked players are able to shot call, Some have to follow others because they cannot think in the way required.
High rank does not mean high skilled in every possible way.
It is very important to understand this point because if something requires intelligence some people are just not going to be capable regardless of how well they play with some other hero and regardless of their 95% accuracy.
Symmetra has a skillset that isn’t going to work for everyone, If you can’t see any value in being able to force the enemy to reposition or splitting a fight by using her ultimate you are not going to get value out of her ultimate, Ultimates are a big part of this game.
Low pick rate does not necessarily mean boring or awful, It can also be “I am personally not good with it so I personally wont use it”