When you start bjj you begin to notice how soft you were previously. This especially applies to the neck as most people in modern age spend a lot of the time working by a computer screen or staring into a smart device.
This is of course besides not being used to a variety of chokes, controls and even cranks that inevitably get applied to the neck at some point during brazilian jiu-jitsu training.
Naturally, taking care of the neck quickly becomes integral because while there is a variety of injuries to the limbs none of them have the potential to be as debilitating as the neck and back injuries.
BJJ black belt Mike Palladino shows his neck strength strengthening routine: