Why do normal captchas still exists? There are many (also big) services that still have these number and letter captchas. Every programmer could crack them in seconds...

Because some people don't want to use Google's and light not have the time to look for others.

Making your own captcha isn't difficult either. It wouldn't be great, but it would catch non-serious botters.

@Root hm yeah maybe

Training very simple AIs?

And your "advanced" captchas can simply be sent to a captcha farm for like 10000 solves for a dollar. It does not make a real difference.

To prevent casual spamming

To make script kiddies life that little more difficult.

Then you go to recaptcha to make their life miserable.

Then they go to a bot farm and make your life miserable at their own cost.

There is nothing wrong with the basic letter/number generation unless you become a target.

@C0D4 so in other words they are useless because if someone tries to crack them he will be able to do so easily

@reij not useless, a deterrent.
It adds a cost to getting around it.