Earlier quoted context omitted.
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)
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."
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.