This doesn't follow. Not even fighter jets were inherently unstable before modern control electronics. Using the electronics to make the flight characteristics better is not the same as the airframe being inherently unstable.
Fighter jets are also, in comparison to airliners, not very aerodynamically efficient. They can be fast but burn lots of fuel while doing so. They are like a motorcycle compared to a bus.
Until they hit an AOA that puts the tail in the wind shadow of the wings. Then some will pancake. They can slip sideways into scary turns/dives and will not recover on their own. And they are delicate. It doesn't take too much force to twist them out of shape.
In a deep stall you can’t recover from, it’s because the aircraft’s stability is greater than its control authority, not because it’s unstable.
The only really stable commercial aircraft are, perhaps, the bushplanes. They are not fast and not fuel efficient over any real distance.