1) Getting natural gas plumbed to your generator is expensive.
2) If you're running this generator for an extended period of time, things have pretty much by definition gone to shit and aren't working as designed. You have a lot fewer dependencies to go fill a couple of jerrycans with gas at the nearest gas station (that has both gas and power to pump it [0]) than you have to restore piped natural gas service to your property.
[0] And if a gas station loses power, getting it hooked back up restores its utility to everyone, whereas restoring power or natural gas service to a home only restores its utility to the person living there. Prioritizing gas stations over private homes makes a lot of sense.