A video I saw said that this gun took them 3 years to develop because they poured so much into reliability. Apparently 1 year is the standard for all the other model pistols.
To be honest, how much development really goes into a generation change on a Glock. New texture, remove or add finger grooves and tweak the action a bit. The basic engineering has been done for decades. This was new ground for them, so they took their time to get it right. I like that in a company.