Indeed, Bitcoin is still relatively small. Its money supply (aka "market cap") isn't even 2.5% of the USD M1 money supply. Not to count all other fiat currencies.
That it's even grown to be even that large is surprising.
Honestly, when I first heard of it in ~2011 I never expected it to grow as much as it did. I thought it would probably remain a small experiment confined to nerds and hackers. When it first started hitting mainstream news a few years later I was quite amazed. And while I'm here amazed at how far it got, critics are dismissing it because it hasn't replaced USD yet...