Lightning, storm wind/waves, failure from factory defects in hoses/seacocks/electrical components, electric fires in general, other people collide, vandalism....etc...etc...
All can be mitigated but to what degree and what would still be the outcome..... even on land in the middle of nowhere it would be relatively safe there.....but when on the water, too many factors creep up with you not able to control them.
Sure a lot of boaters go through a lifetime of no claims and just minor issues....but who is gonna bet serious money on sometimes near uncontrollable events?
You can mitigate but you can not even approach statistical zero or any type zero and even if the risk is 1% most of us don't want to risk that.
You own a house in a gated community with security, do you then go without insurance?
I've seen storms and even hurricanes do little damage but spin off small tornadoes and they take out one house and don't touch the surrounding houses or one small section of docks and miss all others. Lightning could strike anywhere at anytime.
I've owned boats for 38 years and never filed a claim. Several boats now. Yet, I'll never go uninsured and glad to share with those who have had claims. I know a couple on this forum who I would consider very diligent and careful and safe but have had claims and I have no problem sharing indirectly some of that incurred expense.
All insurance is shared risk-property, health and life are. I guess centuries ago and prior to insurance it was left to neighbors to pitch in and help, but they didn't always come through and people lost everything. I prefer insurance as the answer.