It is not only possible, but often encouraged to have more than one life insurance policy (for example, the first term policy you have, plus a new one as your financial needs have changed, plus one at work, plus one that may come "included" with your credit union membership, etc).
Why can you not have more than one car or homeowners' insurance policy with different carriers? For example, why not have a policy with Allstate and State Farm on the same property?
What is the legal reasoning behind such a rule at the state level in the US?
Note - this is not a question of whether or not it makes financial sense to the potential holder of said policies.