1-down and 4-up shifting pattern in motorbikes

Actually, there is a specific reason why neutral ended up between first and second gear when motorcycle controls were standardized in 1975: SAFETY.
In the 60s and 70s, there was a growing trend toward placing neutral below first gear. My nephew, for example, had a Kawasaki 100 with a "4 up" shift pattern (N,1,2,3,4). As this shift pattern gained popularity, more and more motorcyclists were developing the tendency to instictively shift the bike all the way down into neutral as they slowed, sometimes accidentally, but most times intentionally. The idea was that you could stay in neutral at a light or stop sign, then clutch into gear and start rolling again when right-of-way was established. The habit was obviously flawed, and riders started getting hurt.
The vast majority of injuries were caused when a bike was inadvertently upshifted from neutral into first gear at a fast coast. The resultant engine breaking caused instant rear wheel lockups, which in turn caused crashes. The mechanical aspects of neutral's location also caused various runability and logistical problems, as well.
By locating neutral between first and second gears, the severity of engine breaking in the event of accidental upshift was reduced, as well as making neutral a relative inconvenience, rather than something riders depended on. It also made first gear the natural first position in the gear box, which is where the transmission should be adjusted whenever the bike is stopped in traffic anyway.—Tim Kreitz Courtesy #-Link-Snipped-#

The real reason is that the shift pattern was mandated in the United States Code of Federal regulations under Title 49. As of 1975, for manual shift motorcycles the shift lever must be on the left, first gear must be all the way down, the remaining gears must be sequentially up, and the location of neutral is not specified. Track bikes, offroad bikes, and bikes not intended for the US market do not have to follow this pattern.