If you have $100 on your bank account today then you've got incentives to spend or invest it soon because it's slowly losing value because of inflation, your $100 will probably buy you fewer goods and services in the future that it does now.

Now if you have BTC100 on your wallet and you believe that Bitcoin will succeed as a currency then you know for a fact that these bitcoins will be more valuable in the future than they are now (because the demand will grow but the supply is capped). Ergo you have strong incentives to hoard your bitcoins and not spend or invest them. Your savings gain value without actually being invested in anything. They don't contribute to the economy, they don't fund anything.

I don't understand why most cryptocurrency enthusiasts don't see a huge problem in this. How will you get a loan to start your company in the bitcoin world? Who would want to take such a risk when they'll keep getting richer by not doing anything at all? You'd have to promise them ridiculously high returns (higher than bitcoin's deflation at least). The rich gets richer by virtue of being rich, the poor needs to buy food and basic utilities so they can't save their coins to become rich. Basically what we have today, only worse.