How many times has LP been hacked?
Notifying customers of a breach is a much more ethical approach than sitting on the information. In some countries it is even mandetory to report breaches to affected users, which I personally think is better than not doing it.
The activity in 2011 was never confirmed to be a breach. It was a overcautious response on LastPass's part after seeing an outlier in the logs. The investigating party gave a report saying they couldn't find anything, and the CEO later gave a statement saying they overreacted to an outliter out of an abundance of caution.