It makes no sense for the lost transit fees to be paid by the insurance companies as most vessels waited the 6-day period and then got to traverse the canal with some days in delay (so Egypt still got that money).
In the end the claim seems exaggerate and might be indicative of Egypt's lack of focus on long term relations. It's one thing to pay 500'000 USD for a passage, but if I know that I have a 0.05% probability of paying 1 billion dollars (which is another 500'000 USD expected payout on average) then surrounding Africa without any fees is all of a sudden a lot more attractive.