In Lev. 19:18, why is it worded with רֵעַ, the word translated *neighbor* rather than the word שָׁכֵן

In Lev. 19:18, why is it worded with רֵעַ, the word translated neighbor, rather than the word שָׁכֵן? Both occur throughout the books of the Old Testament and aren’t isolated to a particular period of time. The common word in modern Hebre…