why cant i turn off 2 step verification?

Two step or Two factor?

For two-factor authentication,

See Two-factor authentication for Apple ID https://support.apple.com/en-us/HT204915 and more specifically the section entitled Can I turn off two-factor authentication after I’ve turned it on? This section says: 

"If you recently updated your account, you can unenroll within two weeks of enrollment. Just open your enrollment confirmation email and click the link to return to your previous security settings. Keep in mind, this makes your account less secure and means that you can't use features that require higher security."

This quote emphasizes the security-related importance of two-factor authentication. I would not turn it off even if you are able to. Another reason for not turning it off is that if you use two-factor authentication, then you no longer will have a need for security questions. They are turned off when two-factor authentication is activated.

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For two-step,

See Two-step verification for Apple ID https://support.apple.com/en-us/HT204152

To turn it off:

Make sure that you're still signed in to iCloud on each of your devices. You might be asked for your Apple ID password.

1. Sign in to your Apple ID account page.
2. In the Security section, Click Edit.
3. Click Turn Off two-step verification. Click again to confirm.
4. Create new security questions and verify your date of birth.

You'll get an email confirming that two-step verification for your Apple ID is off.