By the same obscurity-based argument, it's probably easier to just roll your own Captcha than installing/integrating/depending on a third-party library.

Please prove you're a human by typing "cat" below

Exactly. This isn't an end all be all, but it does up the security on your site.

It's like when you lock your bike, a focused attacker can open any lock with the right tools, but that shouldn't stop you from locking and using secondary deterrents like anti-theft skewers, or my favorite, simply locking it next to a nicer bike with a worse lock.

That's what I thought, until somebody reverse engineered the registration mechanism on my personal site which runs software I've written. I ended up having to turn registration off as I didn't have time to fix it properly.

This is also an argument against using a standardized module like this, at least once it gains wider adoption.