No caller IDs being used by employers. Is this a new thing?

I'm job hunting right now and apply on a bunch of different websites to widen my search. Wherever possible, I specify that I prefer communication by email.

Recently, I've been getting a TON (multiple a day) of no caller ID calls. Some leave voice mails, some don't. My phone automatically flags these calls as scam calls. There have been a few times where the voicemail has said to call them back with the number they called with, but you can't call a no caller ID back (I've tried).

Is this the new thing? If so, why? They must know these types of calls get flagged by most phones. I managed to email a contact at a company I was applying for and told them about the no caller ID thing (the voicemail told me to call them back on that number to talk) and the woman said 'oh do you think that's why we haven't been getting any call backs?' OH YOU THINK??