Have none? Probably not that many (although Flickr probably is comparatively interesting for a large part of that demographic). Willing to share with a random service on the other hand...
It's a security measure which protects the unlimited storage feature, among other things.
What if someone wants to use random burner accounts to store gigabytes of child pornography?
That's a lot harder to achieve if they have to buy a burner mobile phone for each account, and each burner phone has the potential to be tracked to the point of sale to use video and other techniques to catch the predator.
Mobile number verification is a very cheap and powerful way to cut out the vast majority of bad actors.
Phone number requirements is a very effective tool of surveillance and surveillance capitalism but it's also incredibly effective at keeping potential users out of your business.
Have a look at the popularity of online services providing phone numbers for verification purpose.
Okay, WhatsApp is #2 service: Requires Phone Number verification
Youtube, #3: No phone number verification, service is full of fake accounts, trolling, bigotry, and state propaganda and is seen as one of the worst communities in internet history
#4: Facebook Messenger: Phone Number Verification
#5: WeChat: Phone Number Verification
#6: QQ: Optional phone verification, but operated under am authoritarian government which strictly regulates user bases, use of networks, messages made, etc. (AKA they hire armies of people to manually monitor and police the service)
