Since the cost of lifetime memberships is often less than 10 years paid out individually, it's a better deal for people who use the membership now and are active enough to use it for that time period. People who buy the membership but lose interest don't get the same benefits.
One potential risk with a lifetime membership is that the organization selling the subscriptions doesn't stay in business for the lifetime of the members. In those cases, the lifetime membership becomes worthless. Also, people who lose interest or involvement with the organization fail to use their benefits as time goes by, keeping them from getting the full benefit.
One example is SPIE, the international society for optics and photonics. A lifetime individual membership to the organization costs $995, as of April 2015. This gives the member access to 10 journal article downloads or digital library proceedings, as well as an online subscription to the association journal of choice, discounted registration for conferences, courses and publication purposes. Moreover, this comes with access to a complimentary online SPIE course.
Members also get an online member directory, as well as other professional resources designed to advance their network and career. Active professionals in this field who are at least a decade from retirement benefit from the lifetime membership, while others more peripherally involved or closer to retirement might choose a different option.