While I agree that const/let is a useful convention for communicating mutability, it isn't nearly a big enough deal to warrant the attention it receives from the community.
It's not just const/let; I rarely make a front end PR that isn't bike-shedded to death over subjective styling choices, single quotes vs double quotes, etc. It often feels like conforming to flavor-of-the-week, subjective decrees from frontend trendsetters is more important than the substantive work that your code is doing.