Cost. Useful life. I thought about an off grid system. Batteries are expensive. Also, unless you live in a dry place in the equator, You'll need to account for things like winter, long rainy spells, so either you add more batteries to account for multiple days (weeks? months?) of low generation, or you'll need a diesel/gas generator, or have a hybrid system instead, which basically means you're using the utilities gas generator instead.

Then, subsides are drying up. Systems have a useful life, your panels can be damaged by storms, for maximizing battery life you need to ensure you don't discharge it below 20%, and neither charge it over 100%.

So, in the end, the grid needs to be there anyway, but as most grid costs are fixed, whenever you use it now, it is going to be more expensive.