What your talking about is rate limiting. And pretty much every social media already does that. The issue with adding requirements like phone number etc, is that it also makes it more difficult and annoying for regular users. Besides, bot account owners litteraly have large amounts of fake valid mobile phone numbers they can use to "verify" their bot accounts. Then they also use change their ip addresses, so rate limiting can't be enforced. Instagram also has a massive bot issue, but its just an endless amount of bot accounts, not just one that is spamming all over the place.

Adding a fake 10 second delay would stop absolutely nothing and make the experience even worse for regular users.