If we stop calling the Apps and call it Software, would that make more sense to you?
When you purchase a digital product or service, whether it is software, music, or a movie.
It is for your use alone.
You sign an agreement with each purchase, which no one reads, but simply put, you have use of a digital product. No permission to give away or sell is granted. In order for Apple to honor this agreement with artists and programmers, it restricts purchases to the Apple ID used to make the purchase.
You may move your purchases to your devices as you please, with your Apple ID
A new device doesn't mean loss of my purchases.
If my computer crashes, my iPad breaks or my iPod is lost or stolen, I can download my music, apps and other iTunes purchases to a new device.....
With my Apple ID.
If you have spent a lot of money on music and apps from iTunes, you will be very glad to know you can recover that content, with your Apple ID. After all you paid for the use.
That said...
Within a family, you can use one Apple ID and different iCloud accounts to share purchases, but sync to your device only your content. You can sign in and approve an update on another family members device to update an app purchased with your Apple ID.