It removes the ability to directly connect to your existing USB-A devices without overcoming that roadblock. You could argue the exact same that the front USB-C 3.2 ports don't add any functionality over USB-A 3.2. It adds an obstacle to be overcome.Removing the USB-A connector does not remove any functionality. It’s quite simple and very inexpensive to use new cables or converters. Software-wise, the connector is no problem; USB is USB no matter which connector you use.
Apple has migrated their entire ecosystem to USB-C and the computing industry is doing the same. As someone who travels frequently, it is so much nicer to have all of my devices use the same connector. I usually travel with Bose headphones, AirPods, and Apple Watch, phone, iPad and sometimes my MacBook Pro and my Canon camera. ALL of these devices use USB-C, although the watch needs that special magnetic USB-C cable. At home I have a dock with a USB-A for when I use an old memory stick and for my keyboard/mouse receiver.
I also prefer that devices are moving to USB-C (even if Apple had to be forced to do so by legislation). But many desktop peripherals and devices are still overwhemlingly USB-A, including many of the new ones. This alone means USB-A is not dead as some wish it were.
How would you be affected in any way if Apple included a pair of USB-A ports on the Mini? You say it's trivial to replace all your cables or use adapters, but far more trivial for you to just not use the ports if you don't want to.