Have you ever been to Wall Street? The workers in the back offices are a combination of old and slow and young and dumb. It takes them at least 3 days to get it right.
Because it takes time to transfer all those stock certificates,log them, hand them to to couriers so they can go on bike or walk to the other firm, separate the securities, transfer them etc.. Lots of paperwork and those Stock certificates pile up fast.
I've always been confused with settlements or forget about them altogether. Is it as if something physical would have to take place in order for your trade to settle. As if a coin would take three days to reach the bottom of your piggibank. Ridiculous. But as Wall Steet is king, others take it and make it the standard.
It's been a while since I've checked but how long does it take these days for a check to clear? Last I knew you could have 1/3 of the funds immediately if you had the same amount in the bank, then you could have another third in a few days, then some arbritrary date in the future (like 7 days) you could have the rest of the funds. Whazzup wid dat? And sheesh reporting transactions of 10k like that is "big" money to the trillion dollar fed.
I do (well, I used to before blowing up my account ) trade futures and one thing I like is precisely the immediate settlement. On the other hand I find it awkward with futures that you get different commissions from the same broker depending on what software or connection you use, the need for a clearing agent and so on.
Anyone with a pulse can trade futures. And get wiped out in no time... . Best thing to do is use the simulator till you're constantly profitable. The thing with futes is that if you do well you are done for the day even before the opening bell rings. This is something that poked my greed, but I went in too early and lost my shirt.