I found LOST late in the game, watched it all like for the first time 3 years ago. Found a great article / interview that explained why it "fell off" towards the end with those recap , flashback like episodes.
Due to its popularity they then sold the contract on an episode basis to the UK and the season(s) at the time were not planned to go that long. They couldnt alter or renegotiate contract so they made those "filler" (as i call them) episodes to oblige the contract. Once i read that, it made more sense as they felt so unneeded.