Why I can’t receive email address verification code of an iCloud
Why I can’t receive email verification code on my iCloud account
If you are asking why the code can't be sent by email, we are users like you, not Apple employees, so we don't no why Apple didn't make that an option.
Are you trying ti sign in and need a verification code? See if anything here helps. If necessary, you can use account recovery as explained in the link at bottom of the article.
Verification code - how to get one and sign in with two-factor authentication.