You dont get it...
If you had herbs that you could have sold for lets say 25g each stack.
Then you instead make cards and get ~7g / stack of herbs from opening the cards.
And you call that a good profit? Getting 1/4 of what you would have gained if you sold the herbs on ah.
So for that 6000 that you gained you would have gained maybe 24000 if you actually sold the herbs on ah. And if it is too hard to sell all those herbs, then it is just to spread out and get herbs+ore+low lvl mats + anything else that is worth botting. Or using a crafting profession and AH bot.