Why would it be particularly easier to manipulate bitcoin pricing over other stocks/securities? Simply because the authorities don't understand it yet, or something to do with the nature of crypto-currency itself?
According to some blockchain site[0] the average transaction volume for BTC is something like $2.25m USD equivalent
For comparison, on an average day, SPY[1], which is just one security (albeit a popular one) trades something around $17,160m (e.g. $17.16b).
[0] https://blockchain.info/charts/estimated-transaction-volume-...
Sure, but there are also laws and regulations that limit what you can do with stocks on a real exchange: https://en.wikipedia.org/wiki/Microcap_stock_fraud
> won't this problem go away as BTC gets more popular?
Maybe. It would have to get a lot more popular, and a lot more legitimate and regulated. At that point, it's lost all the cyberpunk appeal, and it's just another speculative asset.