I'd say that is the only good explanation on why they are the only eCommerce site I know of that requires you to give them a credit card before they will estimate shipping.
I just tried to retest this to verify it hasn't changed in an incognito window (so I was "anonymous"). It would not even allow me to add to cart without giving a valid phone number. So, I could not even get far enough to verify if I could get a shipping estimate without entering a credit card number.
EDIT: With same browser, I tried to add another item. It let me. But, when I tried to view my cart, wanted me to log in or create an account, which required an email or mobile number. I didn't get passed the email verification, so I changed it to a valid email address I could receive email to:
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It then wanted my
full valid address for shipping. Not just a zip code to estimate. OK, so I gave it Investigator Joe's address. And... we're back to it demanding a phone number. Still no shipping estimate, even though it has far more the info it needs to provide it.
I gave it Investigator Joe's phone number, which didn't have to be a verifiable mobile number this time. And finally, got a shipping estimate so I can compare the true cost of this item to the thousands more just like it:
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Congratulations, you no longer need to give them your credit card number to get a shipping estimate. You do have to give them a valid email or mobile number which you have to receive their code at, your full address, and your phone number if you gave them an email the first time.