Why is so large a range of IPv4 addresses assigned to
It comes from RFC 990, pg 5, under "Special Addresses":
The class A network number 127 is assigned the "loopback" function, that is, a datagram sent by a higher level protocol to a network 127 address should loop back inside the host. No datagram "sent" to a network 127 address should ever appear on any network anywhere.
At the time (1986), the internet was completely classful and nobody really gave much thought to allocating this much space to the loopback address. Thus, the loopback got an entire Class A network.