Isn't it very possible that the seclusion that the Pope will go into after his official date and time of resignation is until there is a newly elected Pope? By all accounts that I'm familiar with, once he steps down, until a new Pope is elected, its a state of "sede vacante"
"The current regulations regarding a papal interregnum—that is, a sede vacante ("vacant seat")—were promulgated by John Paul II in his 1996 document Universi Dominici Gregis. During the "sede vacante" period, the College of Cardinals is collectively responsible for the government of the Church and of the Vatican itself, under the direction of the Camerlengo of the Holy Roman Church;"
Pope - Wikipedia, the free encyclopedia
With this in mind, it makes sense that during this period, Benedict would go into seclusion and have no contact with anyone so as to assure that during this interim, he was not involved in any way. As this is the first time a Pope has resigned in centuries, there's no precedence for the interim period of a retired Pope so perhaps this is to ensure that the same conditions exist for a papal election as it would be on the death of a Pope, he's voluntarily going into seclusion.
I'm sure that once a new Pope is elected, he will be out and about as his health permits and enjoy a peaceful retirement.