when they bought the 100 pounds of weed?

Decided to look at the extended scenes in another site and on theatrical the fbi says the will launder mpney with drugs and go gamble etc on the extended they do it instead of explaing it

So the money can't be traced. The more it's passed off, the further they are from it, the better. There are many reasons to "Wash" it up. A bank gets robbed for $100k, the Cops knock on your door, you have $100k... Sound like a good idea? Maybe even sequential... Get as far away as you can

I don't understand, you seem to have actually answered your own question...the point of buying and selling was, as you stated...to launder the money.