the problem is that you are falling into the same trap the FSF did with GPLv3.
you either thing that
A) everyone agrees with you on this topic (hint, not everyone does, a lot of people are Ok with the idea of a project selling proprietary licences if it funds the opensource code)
B) this is such a critical item that it's worth having many people not use the license, or convert from it to GPL so that they can then sell the proprietary licenses.
and if you can't make that conversion to GPL to bypass the restriction, then you are imposing an additional restriction to what the GPL includes and are not GPL compatible)
Many times projects start off under one license, and it's only years later that they decide to raise money by selling GPL exceptions. In many cases, the uses that the code then gets put to would probably be legal even under the GPL, except for creating what would effectively be a mirror of an obsolete version of the source (unmodified code compiled and shipped in an appliance for example)
So this is a provision that is controversial, and can be pretty trivially bypassed, why is it so valuable again?