Don't underestimate the cost of upkeep on a large scale backup system like you'd need for a commercial building. It costs tens of thousands to install in the first place, consumes a significant amount of valuable space for which you pay rent/taxes, in Seattle for example commercial rent is over $41/sq-ft/yr so if we conservatively say an 8'x10' room for the backup generator or UPS that's over $3k/yr just to rent the space. Then you've got to either have a maintenance guy who is qualified to work on it or hire somebody out on a regular basis. Generators need oil changes, cooling system service, and other scheduled maintenance, repairs and regular test runs. UPS systems need battery maintenance and checks, occasionally need new batteries which cost many thousands of dollars. You've also got the additional hazards of stored energy on the premises, either fuel or electricity stored in batteries. Unless you deal with frequent outages, have life critical equipment or valuable inventory that will be ruined by a brief outage, it's more economical to just shut down when power is lost.
We had a large UPS at a former job and it was expensive to maintain and caused at least two outages that I recall. At some point it was deemed inadequate for the load it was supporting and they spent another $50K or so replacing it with a larger unit. I'm not sure why they had it at all, I only remember there being one or two power outages in the more than 10 years I worked there. A UPS only provides power for 10-20 minutes in most cases anyway so it's only there to let you shut down equipment properly, you don't just keep going and hope the power comes back in time.