Rigged how? Isn't a major point of blockchain its unriggability?
S&P 500 E-mini futures have a notional value of roughly $147,000 right now, and on average, 1-2 million contracts change hands daily.
On average, about 35 billion dollars of SPY, a single S&P 500 ETF is traded daily.
It's hard to find accurate BTC average daily volume numbers, but probably somewhere between 1 and 10 billion dollars daily.
So yes, bitcoin is an extremely thin market compared to the market depth of 2 extremely liquid assets, both of which pale in comparison to the 550 billion USD daily volume of the treasuries market.
BTC does have the tightest bid/ask spread of pretty much any asset that is traded, as a percentage of the asset's value. It's typically a penny to a few cents on the major exchanges, which is a few thousandths of a percent.
Very little blockchain activity happens “on chain”, and absolutely none of the buying/selling to and from other currencies (including USD) does, because thats not possible. Instead most activity happens on exchanges, which hold onto coins for the user and track account balance in a SQL database just like a traditional exchange. Only if a user moves between exchanges or takes possession of their own coins (a rare occurrence) does an on chain transaction happen, otherwise the rest happens in a SQL database somewhere.
These exchanges are absolutely full of straight up fraud, with some analysts claiming up to 95% faked trade volume. Most exchanges trade on their own account, sometimes badly, and the seediest didn’t even require that you create 2 accounts to wash trade. In this case the on chain transactions aren’t rigged, but the price sure is.
Note: these are the exchanges that also famously get robbed (or “robbed”) and go bankrupt with their clients money. Examples famously include Quadrigacx, Mt. Gox, and others.
that sounds a bit FUD-dy. 51% allows you to make a double-spend, not "absolutely rig" the blockchain. even with 100% hashrate you won't be able to spend bitcoins without having a private key.