I believe that's because these numbers are not real numbers. It seems these scammers have figured out a way to use the internet to make calls, disguising their identity and location.
There are so many scammers doing it.
I don't understand the technicalities of it, but that's what I think these are: computer generated phone numbers.
I've noticed some of these companies have hundreds of them all with one digit difference between all of them. So the software is simply going down the list.
Somehow we have got onto that list.
We give our details to so many people, who knows who has given our details, but our details are out there.
I am absolutely convinced the telcos have multiple and ongoing leaks of information. They either know and don't care, or it's so endemic they can't control it.
I got a new phone number to stop this - and it didn't work. Whoever was calling knew things that were only connected to me. Somehow they knew the new phone number was mine. They could only have got that from a telco because only the telco had the information.

Caller: Wine Group from Victoria

I do not drink wine but insistent I should take up a great offer, up to 80% off. States my preference for Shiraz! Where do they get my number from?

Caller: The wine group

Says it's someone from the wine group I don't even drink wouldn't stop calling

I answered, but there was no one on the other end, I waited for 5 seconds, then hung up.

Caller: Wine company

It is a robot call form wine company.It's automatic response sounds and react like human. Have fun.

If they're not on my mobile numbers list l don't answer!
Most come up with a spam or similar warming while ringing, l then block. But this number came with no warning.
I let it ring out then check via the web, sure enough here is a list of complaints!
If nothing, l might ring back not displaying my mobile number to them.
Now blocked! Scum.

Caller: James from the wine group

I don't know how he got the number just hung up straight

Just in another another rude unknown caller who hangs up. If you’re not in my contacts I will not answer your call. I will block this number and any other number that they try to phone from as these type of people ring from numerous numbers

Caller: Wine Group

No matter how many times I block, I keep getting text messages and calls from them!
they are in big trouble, see story on spamming consumers - https://www.news.com.au/finance/business/retail/the-wine-group-fined-more-than-200k-for-spamming-customers-with-texts-calls/news-story/7a6b49d5a7fc134758b7acc564eee9eb

Scumbag

Caller: Scammer

I called back and the message said "the number you have dialed is not in service!"

Missed call, called back and got "your call is important to us, please hold the line to speak to the next available agent". Then hung up after a few seconds. It's not a personal phone number.