Another possible contributing factor is that Mercury/mercury is a capitonym[0] in that it changes its understood meaning via capitalization, which is obviously

Another possible contributing factor is that Mercury/mercury is a capitonym[0] in that it changes its understood meaning via capitalization, which is obviously obscured when it's used in a headline or as the first word in a sentence. [0]: https://en.wikipedia.org/wiki/Capitonym https://en.wikipedia.org/wiki/Capitonym