1) Worrying about something highly unlikely to happen is the very definition of lack of bitochon.
2) Also it makes more financial sense theoretically for the Kehilla to support those cases where a parent is tragically niftar young, than for everyone in the Kehilla to pay for life insurance. If this wasn’t true then the insurance companies would be running a loss. If everyone would pay the amount they pay life insurance into a fund for this purpose, the fund would be able to provide the same amount of money to these unfortunate families, and have a lot left over (equal to the insurance company’s profit margin). That is the idea of Areivim if I remembered the name right. If I’m not mistaken Areivim has the haskomo of Gedolim who don’t like normal life insurance, as the monies paid to them are considered tzedoko to those families who need it, even though the donations make your own family eligible for similar help (I think you can even pay from Maaser).
3) Finally in many countries there is a generous welfare scheme. If there is life insurance, the family may not be eligible for these benefits. So part of the premiums the family paid goes to saving the government money. Whereas if the Kehilla would pitch in when needed, the welfare programs could be used and the Kehilla would only need to top this up. I imagine the same is true of Areivim if the people who set it up thought of this.