you basically hit the nail on the head.  in fact, I just wrote this yesterday on another post regarding a "steemit marketplace":

>I've thought about this for years as well, but the issue is always about gaining traction and capturing that certain "je ne sais quoi". I've also tried alternative sites like offerup. Good luck trying to find what you want at a reasonable price (including a buyer, if you're selling something) anywhere except ebay (and maybe craigslist, though I personally haven't had much luck there myself). One thing ebay's definitely got right on (besides the liquidity) is the trust factor as well (which of course, leads to even more liquidity, causing a reflexive feedback loop). **It often generally feels almost as safe as buying directly from a store.**

>So, with all that in mind, any thoughts as to why PeerHub isn't quite cutting it?

Link: <a href="https://steemit.com/steem/@matt-a/why-don-t-we-have-a-steem-marketplace-100-powered-up-post">Why Don't We Have A Steem Marketplace?!</a>

And, of course, if you're dealing with billions of dollars, how much of that would you be willing to risk in crypto?  In a big bank or brokerage firm, with the exception of SHTF-type events, you generally have some degree of insurance protection and a "certain" margin of safety.  In crypto, make a security slip-up and your recourse is all but zilch (with the exception, perhaps, of the "lucky" SOBs that were made whole during the Ethereum / ETH Classic hard-fork debacle).