I've noticed many browsergame bots, for all sorts of games.

Assuming that these games aren't flash, or Java, why aren't userscripts used to write these bots? So many of these bots are standalone programs written in AutoIT or C#, that hook into the browser or process GET/POST requests. That seems like an awful lot of trouble to go to, and it's easier to thwart by the game administrators. Surely, userscripts are easier?

Things like jQuery make pages very easy to interact with, and obviously useragents, cookies, sessions, etc you wouldn't need to worry about because it's in browser.

Full standalone applications go to a lot of trouble, by trying to simulate a browser.
AutoIT is halfway there, by hooking into the browser, but it's still limited because it physically moves the mouse (usually).

Userscripts can run in many instances over many browsers, and would be much more concise to perform the required bot operations for a browser game, and yet they are hardly ever the weapon of choice. Why?