why is GOogle asking for my cell phone # when trying to sign into Google maps?

trying to sign into Google Maps i was asked for my email address and password. I entered it and was then told to enter the code that had been sent to my email. After three more attempts in futility of entering email address, password and 4 different verification codes it insisted on entering my mobile phone # which i am very reluctant to give to Google. After all these attempts I was locked out - please advise why Google are insisting on having a mobile phone number to "sign-in" to Google Maps