The point is that as an architect you can be very confident that those frameworks will be solid, well maintained and documented and quite importantly well integ

The point is that as an architect you can be very confident that those frameworks will be solid, well maintained and documented and quite importantly well integrated with everything else in the default stack now and in the future. You can also be confident that in the future you will be able to find developers with experience using the default stack. I could bore you with quite a few personal anecdotes that back up my opinions. Of course there are going to be exceptions to this but as a general rule, taking into account all dimensions of the decision, the default stack is the rational choice.