It's probably because the Nest is designed for use in a residential building. The use case of commercial HVAC is not even close to the same. Most commercial HVAC systems are designed, sized, and ran in a completely different manner than a typical home.
I've heard very very mixed reviews. Several direct friends of mine have installed them and gotten very poor results. I think much of it depends on the predictability of your time at home/away and the location of the thermostat itself to sense activity.
My distilled opinion is that they are not significantly better than a simple programmable thermostat for most people.
I have two Nest thermostats (one upstairs, one down) and they're one of the best things I've done to my home. Beyond easy programmability and learning, I can easily put it to away via the phone app from anywhere. The AirWave feature has saved me some money too. I have had nothing but a great experience.
I never heard of it before, but it seems like it addresses the major issues I have with programmable thermostats, which is that their UX is invariably like something from the 1960s.
Now if you could disable all that learning crap then we'd be talking.
You can disable that stuff. Once you turn learning off you can use it either as a normal thermostat or as a pre-programmed one.
I actually use our Nest as a normal thermostat that just looks great and can connect with my phone. It's awesome. I also like that it tells us our energy usage relative to everyone else.
I bought it because it's far and away the best looking thermostat out there and because it can connect with my phone. LOVE it for those reasons.