21 million is already a lot and if it would be higher then the value that it will have today is going to be lower. That doesn't matter if it's only 21 million because we can have it even in the smallest portion.
And that's making bitcoin more reliable and in-demand.
The supply is already higher than 21 million, have you ever asked your selves why they are 8 zeros after the point? That's why people need to see bitcoins from its basic unit called 'Satoshis', so, we don't have to worry about the amount of bitcoin.