Some licenses require a copy of the license along with the game's distribution. So often you end up with both a credits scene AND a folder with the licenses, you have no real choice then.
Example: MS-PL for game without closed source:
If you distribute any portion of the software in source code form, you may do so only under this license by including a complete copy of this license with your distribution <snip>
Besides, some licenses are way too big to put in a credits section. Some
require like 5-6 lines of text including url's in it
(like the CC4 licenses that have no proper attribution instructions). You don't want that in your scrolling-credits-scene. Most people on the forums seem to just ignore it but technically you would have to at least add an extra text file to the project (referenced in the scrolling credits screen somewhere to make them 'clear') which contains the full credit-details including all required url's, license-copy's, all author's aliases, etc.
But I believe that 80% of the people violate the above and most don't even know it. And probably 90% of the copyright holders don't care anyway and don't even know about it themselves.
Even a SINGLE member+ graphic requires the following credits (M
arch 2014, enigma sample) which is already 2 lines unless you have more than one member+ graphic from the same year:
© 2014 DEGICA Co., LTD;
Artist: VexedEnigma
The other problem here is that you usually want the format like in the movies (artist section, then list of names). You probably don't want "Artist: <name>" and you don't want
The other problem is that you may get something like:
© 2013 DEGICA Co., LTD;
© 2014 DEGICA Co., LTD;
© 2015 DEGICA Co., LTD;
But I'm not sure if you could combine them to just 2015. I think you can.
And the list goes on. So I personally prefer a text file to 'dump' all such credits to keep the ingame one clean. And all people with 'annoyingly large credits' go into the file. Problem solved.