Think of money as a religion for a moment.
A small religion is called a cult. This would be something akin to altcoins.
The most successful religion is called the one true religion. (Mostly by its followers)
Cults come and go. Most of them die without ever ascending to religion status. Some force themselves there like a sci fi religion did that time.
It’s just that for money, these smaller projects die.
Every other form of money, including and especially altcoins, cannot guarantee that.
Why does it matter so much? If a money supply can be inflated for personal gain, then it’s only a matter of time before it’ll happen. The easier it is, the worse it happens.
There can be only one of what Bitcoin is.
Bitcoin is the one true money.