With the generator neutral & ground un-bonded:
If the neutral happens to short to ground and you make contact with the hot while grounded, ouch!
If the hot happens to short to ground and you make contact with the neutral while grounded, ouch!
If bonded then a hot to ground short trips the breaker on overload & a neutral short to ground will trip a GFCI breaker or outlet on ground fault if it is between the short and the bonded source.
That is how I see it. 22 years Naval experience living in a steel pipe (submarine) for 10 of them. The neutral & ground were bonded in that environment.