Your statement can be rephrased as "nobody likes their share of the pie to be decreased".

At first sight, that's seems obvious.

But on closer inspection, it's not so obvious.

For the pie to be useful, you want as many people as possible to have some share.
And you want this pie to be more attractive to people than some other pie.

So you don't want the pie ownership to be too concentrated. Maybe, if you believe in fairness,
you want future generations to have some share of the pie as well.

That's why you want the supply to keep growing. Preferably not by too much though. Just a percent or two per year.
That makes you not lose too much of your share while allowing many more people their fair share....