I understand this is annoying and spoils the game. I have also seen RMT activity and spent a good deal of time reporting them. As others have said it does take time. The main reason SE do not jump on every individual case is because they watch their activities.
See who they trade with, see who they add to friend lists etc. So they can catch more at once. This effects RMT more because they lose a large amount of gil they have stored up, they then have to buy more new copies of the game to get back on their feet again. It also leads them to the people who buy the gil, which obviously removes customers.

If they just jumped on 1 bot at a time they wouldn't be able the gather as much info and have as much of a damaging effect to the RMT business.
What i have explained is quite obviously proved when you look at their posts on the lodestone.

They are on the ball, getting frustrated and throwing round accusations is only going to increase your own frustration and unhappiness with the game and spoil your own enjoyment.