When I tried to comment to a question I was told "you can't comment because your reputation is below 50" and I want to know why they are saying that.
Put simply, if everyone who signed up was able to comment immediately, all the Stack Exchange sites would fill up with spam overnight. I don't think anybody really wants this.
In all seriousness the is no vetting for accounts other than on-site mechanics.
Like a lot of other restrictions this is to limit the amount of damage a malicious actor can do without investing a lot more time and energy than most people will consider worth the pay-off.