The insurance payout amount is based on the cost of the minerals to build the ship. That’s why insurance is so different between regular T1 ships, and T2 and faction ships.
Insurance is sort of a necessary evil that can help ease players into the game, but comes at a cost to the economy. As was said above, as sort of a compromise insurance covers only the mineral cost of ships which means T1 ships are much better covered by insurance than the more powerful T2 and pirate ships (like the Astero).
There is not much you can do about this but plan ahead and not fly what you can’t afford to lose. If you can’t afford to lose your ship, keep it docked and fly an insured T1 ship until you can. It won’t take too long before the cost of an Astero doesn’t seem like much to you.
It may be more accurately to say that Insurance is based off the (equivalent) T1 hull of the class, example: Ishtar will be insured based on the value of the Vexor. So insuring anything other than T1 hulls is more of less a waste as you get next to nothing as payout for Faction, Pirate, T2 or T3 ships.
But if you are taking your t2 cruiser or a Stratios to PvP action. There is a fair chance of loosing it. So Insure it Platimum!
Chance depends on your tactics, but really. Fair fights in EVE is not common.
Insurance costs have changed a few times over the years. Years ago I believe it only looked at regular mineral prices so t2 ships wouldn’t insure for much, but now the insurance will look at moon materials but it also discounts them by a bunch. The moon mats insure but it’s at a pretty big discount, there’s also profit for each stage of refining the moon mats to t2 build components to look at, so there will be a bit more difference between price of building and raw materials. For t3 ships The t3 components also have some value in the insurance system but that is even more discounted. When t3d came out you could insure them for near full value
Looking at the vexor and it’s variants there’s a tiny difference between the vexor and the VNI, Then there is a pretty big difference on the ishtar thanks to all the moon mats, although it’s still way below what it costs to build/buy an ishtar (currently ~300mil in jita).