The why I guess would be to save cost and maybe space. In theory I suppose it could be hacked, but if it's secure enough for the billion iPhones and iPads out there, then it's probably secure enough for practical purposes. Although, iOS is more locked down than macOS, but I believe they share some core foundation, so if the indicator lights function at a deep enough level in the system, then maybe they're equally secure. I suppose we'll see if it ever gets hacked. I'm sure people will be looking for signs of it, and I'm sure it will be huge news.
The hardwired light I'm sure is more secure and maybe even completely unhackable remotely (although I always still cover my cameras because why not), but the hardwired light might be only an extra precaution needed for security at the highest level, like nation state espionage type stuff. That's probably the level at which there is sufficient motivation and resources to make hacking at that deep of a system level possible enough to be a non-ignorable threat. My guess is any of those people buying a Neo will put a camera cover on it.