Why does everybody recommend Dban over more fundamental methods?

The technical reason is it's much more straightforward. When trying to erase data, the last thing you want to do is make a mistake, which is far more likely with a series of commands than running a single program. You might target the wrong drive, or get distracted halfway through, or not perform the steps in the best order. With DBAN, you know for sure that all the drives connected to the machine will be securely erased.

I use it for all the reasons already stated, but I have one BIG additional one. My auditors KNOW what it is and have approved it for fulfilling the secure disposal requirement. Being able to say "We use DBAN" and the auditor going "Ok, lets move on" is worlds better than "I use this custom script" which would trigger, ok let me see it work, Explain each of these commands, wipe a disk and give to me to audit. That's 30 seconds compared to what could be hours and still the possibility of it not getting their ok.

I think mostly because dban actually gives you a GUI and progress bar. DD works, but for some people it could be nerve-wrecking to just type and not see anything happens, until it does. Technically speaking, I think dban has enough features to wipe a drive safely.