If only 5% of the population owns BTC what is the use case?

Serious question: I can’t get over this, fyi I hold a respectable amount of BTC.

So, if 19 million bitcoin are presently “minted” and only 4% of the population are holders….

At max there’ll be 21 million minted equating to approximately 5% of the population. What good is a “currency” that only 5% of the population owns??? Are we going to use it just between each other while 98.2% of the population uses something else???

If the vast majority of merchants do not accept BTC now what would be the catalyst start with only a 1% increase of ownership?

I know I’m missing something but can’t figure it out. Thank you.