Mobile, WiFi and GPS would require a substantially bigger battery to achieve the planned 30 days (I get about 25 days). I guess it wasn't a design goal.
I deeply appreciate the battery life personally. Every time I charge it is an opportunity to forget to put it back on. I can go on a long trip and not worry about packing a charger. I can wear it at night to track sleeping more easily. And probably most importantly, with weeks of life, there's basically zero chance of me being surprised at 9am after leaving the house that my watch is about to die in a couple hours.
The reason Pebble has a chance at success is because they carved out a niche years ago, and for some reason no one decided to occupy it in their absence.
I can vouch for the falsity of this statement. I am more than happy to pay hundreds of dollars for a watch that has weeks of battery life and a great UI. Although there are other watches with long battery life (Garmin, and to a lesser extent Amazfit), their UIs are not good.
Apple and others make watches with nice UIs, but of course the battery life is measured in days, not weeks.
It can still tell you the time. Its primary function is a watch.
At least, that's what quartz watches could manage in the early 90s, as does the clock in my microwave oven from the early 2000s. Why would a modern disconnected device would be any worse?