Travel insurance is designed to protect against unforeseen losses which could potentially happen in the future, not to protect against losses which have already happened. You are only covered for losses which occur “after” the policy effective date.
In addition, travel insurance usually covers trip cancellation for specific perils or events as listed in the policy (i.e. injury, illness or death, etc.) For reasons not listed in the policy, you would need a policy with a “cancel for any reason” option.

Related articles:

• I booked part of my vacation, but not the flight. I would like to purchase travel insurance within the pre-existing condition exclusion waiver period. Do I have to wait until the flight is booked?
• The resort that I will be staying at next week was just damaged by a hurricane. If I cancel my trip now, will I be reimbursed for my pre-paid non-refundable costs?
• If the destination where I will be staying is damaged in a hurricane before my scheduled departure, can I cancel my trip and be reimbursed for my non-refundable costs?
• Where to File a Claim
• Will travel insurance protect me if I must cancel my trip due to the death or illness of a traveling companion's family member?