How do I get my legs to be muscular and defined? Why do I have abs but ugly legs?

I really want my legs to have a lot of muscle definition. I have ab definition and it took such minimal effort but it seems like no matter how much I run and no matter how many squats I do my legs always look like I don't even work out.
How do I get my legs to be muscular and defined? Why do I have abs but ugly legs?
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