The concept of people leaving audio messages _with a reasonable expectation that someone will listen to them_ is (thankfully) dying out, at least among my social circles.
You can leave a message if you want, I'm not going to listen to it. The only entities that make unexpected phone calls are scammers and bots.
Given that I never get ham voice calls, it is reasonable for me to assume that any voice mails that I receive are therefore spam (but, no, you're right, I don't recall ever noticing a spam voice mail. But then I wouldn't notice one, whether it existed or not, because I don't check them)
You must not be in the United States then. Pretty much guaranteed every phone number in the US has received at least one “automobile extended warranty” voicemail.
Still gives me a chuckle. Grow up.