[segfaultbuserr]

Documentation is not the problem. The problem is that, the advertising clause requires ALL promotional materials to include these acknowledgements, for ALL software that has been used in the software. It was not a problem for BSD back then, since UCB was the only developer. But for projects with multiple copyright owners, such as the Linux kernel, a Linux distro poster would contain a thousand lines of acknowledgements, and this is not even counting the packages in the userspace.

[nitrogen]

A modern revisiting would probably require crediting the project as a whole rather than each individual author, and maybe have separate consideration for products that derive from a large number of such projects.

[Xylakant]

The primary problem is that 4-clause BSD is incompatible with the GPL since it adds restrictions to distributing the software (notably the advertising clause)

[iso1631]

GPL3 allows for advertising clauses -- e.g. in flowplayer

https://github.com/flowplayer/flowplayer/blob/dev/LICENSE.md

"The GPL requires that you not remove the Flowplayer logo and copyright notices from the user interface. See section 5.d below."

[Xylakant]

The GNU project disagrees:

This license is also sometimes called the “4-clause BSD license”.

This is a lax, permissive non-copyleft free software license with a serious flaw: the “obnoxious BSD advertising clause”. The flaw is not fatal; that is, it does not render the software nonfree. But it does cause practical problems, including incompatibility with the GNU GPL.

https://www.gnu.org/licenses/license-list.html#OriginalBSD

[iso1631]

https://github.com/flowplayer/flowplayer/blob/dev/LICENSE.md

The Flowplayer Free version is released under the GNU GENERAL PUBLIC LICENSE Version 3 (GPL). The GPL requires that you not remove the Flowplayer logo and copyright notices from the user interface. See section 5.d below.

You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source code under the terms of section 4, provided that you also meet all of these conditions: * If the work has interactive user interfaces, each must display Appropriate Legal Notices;