Language is dynamic and the meaning and spelling of words changes over time.
The expression comes from journalism, hence why lede is preferred. It's something one should not do when writing an article - bury the most important point in the middle of the text.
I heard they used lede to distinguish from (hot) lead. But since linotype has been dead for 50 years this is probably moot now.
Only in American English.
In actuality both "lede" and "lead" are correct. "Lede" is mostly an American and recent respelling of the word "lead" and "lead" still remains the predominantly used term (while "lede" is predominantly an American journalistic spelling).