Because there are consonants that change their sound before an “e”. So, say, the word “chicos” (boys) and “chicas” (girls) should be written as “chiques” in neutral because the c sounds like an s and not like a k with an e in front… but “chiques” doesn’t look like “chicos”… visually it’s not recognizable… while “chicxs” is much easier to parse. So that's why some people prefer the neutral to be written with an x.