In the vast majority of cases, it will be the tour operator and not the travel agent who is offering the free insurance policy though, surely?
Certainly that has always been the case whenever I have booked a holiday where "free" insurance was part of the deal (which seems to be most of the time, these days.)
Generally speaking, a travel agent's role is merely to sell any pre-arranged packages and insurance policies on behalf of a tour operator to a customer; not to organise any elements of the package themselves.
Therefore, in theory, it would be the tour operator who would have to bear the loss of any wasted policy which was taken out - bearing in mind:
A) that the price a tour operator pays to arrange the policies they sell on to customers is likely to be buttons in comparison to the price they sell them on to the public for; and
B) that the deposit you have paid (whatever amount it is set at) is supposed to cover any abortive costs a tour operator incurs should you cancel at any point before you are liable to pay the final balance.
If a tour operator offers low deposits and free insurance as an inducement, then the onus is on them (or the travel agent, if the booking is made through an agency) to make it crystal clear to the customer before they book if there are conditions attached should the customer cancel; otherwise, any penalties they seek to impose after the customer has booked are unenforceable.
As for the travel agents' position in cases such as this, if a travel agent suffers financial loss because they have failed to spell out the terms of a contract properly before the customer signs on the dotted line, then I don't see how this is either the customer's fault, or the customer's problem. Should a tour operator seek to claw back any commission it has paid to a travel agent where a customer cancels for whatever reason, then it seems to me that this is an issue that travel agent and tour operator need to thrash out between themselves. At the end of the day, the travel agent is the agent of the tour operator; not the customer.