The thing to bear in mind with insurance is that you always expect to pay more in your premium than you would expect to get paid from the policy. If you're insuring against a 30 minute delay for a single flight, the cost of the cover will be very close to the amount you would get paid in the event of a delay, since as you observe, such delays are very frequent. For example, if the flight is delayed a quarter of the time, and the payout in the event of the delay is €100, the premium would have to be more than €25. As you've observed, insurers do not include any coverage for such minor delays in their comprehensive travel insurance policies, simply because it is unlikely to make any financial sense for someone to insure against such a common event.
Insurance only makes sense when you are insuring against a relatively rare event which would be financially difficult for you to deal with, and a minor delay does not fall into these parameters.
Having said that, there do seem to be a few products available to insure against shorter delays. Fizzy from Axa and Connect from Chubb both require you to input your flight details and then use delay statistics to calculate your premium. Fizzy pays out from a 2 hour delay, and Connect seems to allow you to vary the delay required for payout from half an hour, but both platforms won't insure every single flight, presumably in cases where good data isn't available or the flight is often delayed. I put details for an upcoming flight I have which is often delayed into Fizzy, and I was offered a €4, €6 or €14 premium for a €50, €70 or €200 payout respectively in the event of a 2 hour delay.
Given the insurer has to make money on this product, I believe you would be better off putting a similar amount of money into a jar each time you fly, and "paying out" to yourself when you get delayed.