It's also. in general, a bad idea to take out insurance where the insurer is the same party as the one whose failure you're trying to insure against.
For small delays the premium will cost more than the value of the cover.
For large delays there's a non-trivial risk that the insurance will also default if the supplier defaults (nowhere is there any promise, let alone proof, of segregated funds able to cover all orders in full if there's a massive problem).
Your thought process would be correct if we had to protect ourselves from a company bankruptcy. Of course that can alsways happen too but its not the biggest concern here.
The reason is simple. Producing ASIC-chips is getting very very cheap after the inital setup-phase. That means after planing, testing etc it basically costs a fraction of the inital costs. And therefore they can afford it easily to "print" some more chips and give them for free.
Thats also the reason they offer to give you free chips and not a free complete miner. Cause those costs stay the same.
So its not so much bankruptcy we have to be afraid. Its the much more likely option that the chips come a little to late. And against THAT risk their insurance could definitly make a difference.