You might also find your answer in the LastPass Enterprise Manual.
Why does LastPass require a Premium charge for the mobile apps?
We give away the majority of our features and service for free, because we sincerely want to make password management accessible for everyone. We've determined that mobile access and a few other advanced features create "added value" for our customers, and the Premium service provides unlimited access to all of those added features.
While we've striven to offer as much as we can for free, our Freemium business model allows us to maintain our service and further its development. We continue to add new features to both the free and Premium services that increase value for our users.