That's half of ALL marriages in the US, not half of first marriages. Only 41% of first marriages end in divorce in the US, and rates are much lower in the EU, and the UK.
I've looked into it several years ago and a product was trialed, but basically you can't insure events that are bound to happen, you need to bolster the insurance pool.
I and a few others don't have any issue abstracting all topics into their economic realities, including the marriage concept that the state offers in its entity catalogue. I think many more people could do that as well, it is just convenient to deflect and pretend marriage isn't about that, convenient for typically one party in any case.
It's not like someone is forcing you to get married. Also 41% as a top line number doesn't tell the whole story. Among college educated Americans the rate is ~29% and falling year over year.
Also prenuptial agreements are a thing for a reason.