As of November 2024, Gmail already had 1.8 billion monthly active users (
Statista). In an earnings call at the end of 2025, Google confirmed that Google Workspace has 3 billion+ monthly active users.
Can you imagine how many accounts get created? They deal with a
ton of spam accounts.
I'm not sure if it's changed, but OpenAI had an absolute phone number requirement when I created an account some years ago, and it was probably for similar reasons. A "cost of entry," so to speak.
Outlook has a similar verification barrier. Also, gatekeeping against VPN users is extremely common—you end up having to solve more captchas on the web, or worse.