Why CB Should Not Include Instantaneous Setting?

If the relay (relay 2) for the secondary side CB (Main CB 2) of the transformer has its instantaneous setting off, how will it make it in time to clear a three-phase fault that would happen in the following zone:

Also if the transformer above (T1) is connected to another bus bar upstream, which is supplied from another transformer upstream of the bus bar, then shouldn't the relay for the primary or secondary side CB of T1 (Main CB 1 or 2) has it's instantaneous on for coordination with the upstream CB (Main CB 1A & 2A) ? Let's assume its a radial power system.

You can't just look at the single lines and figure out coordination from what is upstream / downstream from what. You have to plot the transformer damage curves and look at the circuit breakers' protective relay or trip unit trip curves to pick settings that will be below the damage curve of each transformer, and still coordinate with downstream breakers for faults further down in the system. Doing a relay coordination study is not trivial, but the fundamentals are simple. There are good software packages out there that do most of the graphical work for you once you enter the data for the various system components, but there is still a bit of an art/science to knowing how to use the various protection settings and functions. Take a class in electrical protective relaying and you will see. Also, check out this (free, downloadable) info from GE:

GE - The Art & Science of Protective Relaying

Because instant FIZZ BANG is dramatic and in most cases very very expensive.. Though others will give the tech reason, the practical one is most applicable..