I wanted to meet Perry, why does Disney do the Long Lost Friends thing anyway?
Long Lost Friends is mostly a marketing scheme to draw AP holders/locals/regulars to the park. If the characters appearing are announced in advance, it may even convince people who are avid fans of certain characters and have to make a longer trip to get to the park.
Other than that, it can be a nice little perk to visitors who didn't even know it was happening and introduce kids to characters they might not be familiar with... therefore making them want to see the movie they're from.
But I'd say the main reasons characters are "retired" are casting, costume upkeep, and popularity.
"On these magic shores children at play are for ever beaching their coracles..." J.M. Barrie