That's because most of these people spoof their numbers and just use random numbers. Sometimes they'll even use legit business numbers. I had a number call me one time and when I called the number back, it was a business owner explaining to me that he has been getting calls all day and hasn't called one person.
(570) 828-3122 shows Deleware, PA on caller ID. No message or voice mail left, so "block this call". Thanks 'No Call List' this is the third spam message that has attacked my cell phone in the past couple of weeks.