The mainframes that were byte-addressable (e.g. System/360) were big endian generally. I think this property led to the Motorola decision to use big endian on

The mainframes that were byte-addressable (e.g. System/360) were big endian generally. I think this property led to the Motorola decision to use big endian on the 68000 and, because of its popularity in workstations, the RISC vendors followed suit. MIPS chose to make the endianness selectable by the hardware vendor, and that has become common, with little endian wining these days in ARM implementations.