If a risk is considered very low, but the damage if it goes bad is more than someone who bears this risk wants to have to pay, having an insurance market to collectivise the cost of dealing with it seems generally to be sensible. In this case the absolute risk is also arguably reduced by handling it in this way, if such risk results from the decisions of relatively few parties (e.g. patent trolls) who will be inherently less likely to take on a well-funded underwriter in court who will contest a claim than to choose to pick off individual commercial users who can't afford the legal and management costs of defending against unwarranted claims.
Various insurances for small risks which people probably wouldn't buy individually are also increasingly being used as extra incentives when selling things which people are more likely to want to buy, e.g. system support.