Spelling the word as lede helped copyeditors, typesetters, and others in the business distinguish it from its homograph lead (pronounced \led\ ), which also happened to refer to the thin strip of metal separating lines of type (as in a Linotype machine). Since both uses were likely to come up frequently in a newspaper office, there was a benefit to spelling the two words distinctly.
From Merriam-Webster.com:
Spelling the word as lede helped copyeditors, typesetters, and others in the business distinguish it from its homograph lead (pronounced \led\ ), which also happened to refer to the thin strip of metal separating lines of type (as in a Linotype machine). Since both uses were likely to come up frequently in a newspaper office, there was a benefit to spelling the two words distinctly.