Previous iPhone Back-ups Are Missing

I back up all my devices to my main Mac which is currently a M1 Mac mini and I back up my phone almost monthly. The Mac mini is running the latest software.

I had an issue today with my iPhone 12 mini that meant I had to undertake an 'erase to factory settings' on it.

Luckily before erasing my phone I undertook another backup.

For some reason when I tried to install my back up to my phone the only option available was the last back up I had just undertaken.

The last time I had to do this process was quite some time ago but when I did it I had the options of restoring my phone from all of my previously stored backups.

Any ideas where the other the backups could be or have Apple in their infinite wisdom decided that you can only store the last and latest back up of my mobile devices now?

Please don't tell me just to use the iCloud as I am not interested in giving Apple any more of my money for something I've always been able to do on my computer.