Because the insurer will ask for police and hospital report if the amount is significant. Any serious accident is bound to have at least one of these reports.
If there is no police or hospital report, then the accident is probably minor and the amount is small anyway, then it doesn't matter even if the insurer doesn't pay.
Also if you somehow manage to lie and you get caught, you risk getting charged for insurance fraud.
And lastly, there's always the case where you could be in a coma or you could die, in which case, there's no way for you to lie about it, and your family will get nothing.
Insurers have millions of customers, so I'm sure they know every trick in the book.
Like many travellers, I've also considered riding without licence in the past. But after doing some research and weighing the pros and cons, I decided against it. Instead, I went to get my class 2B licence in Singapore before riding overseas.
Having the proper riding skills is important when riding in unfamiliar places where traffic rules are routinely flouted and traffic conditions are bad. There are times when I find myself thinking "Woah, all those lessons spent practising narrow plank and slalom in the circuit sure came in useful" after encountering some traffic situations.
The peace of mind knowing that I am covered and not breaking the law lets me enjoy my adventures in peace.
How will the insurer know?
Can just say took motorcycle taxi