probably this is because most people (have to/want to) stick to
established and traditional methods. Those companies who offer the
corresponding kits don't need to change their ingredients as long as
the existing ones are selling well. Patent issues should be another
reason why not all possible combination researchers may think of are
available on the market. And in the time of 'publish or perish' none
of those who need to apply the methods dares to develop new ones. Also
because it becomes more and more difficult to combine the necessary
expertise for such developments in one research lab/setting due to its
commonly high specialization.
just some thoughts,
BTW How do you limit shelf-live of your messages?