I think BB franchised Thuney because he wanted 1 more year to look at Froholdt and Cajuste. Since Herron and Onwenu are playing that would seem to confirm that either Herron and Onwenu are "finds", or Froholdt and Cajuste might be busts, or maybe all four will work out and we need to be patient. I think BB and the staff needed another year to figure it out (being patient), and that is why Thuney was franchised, but Thuney will not be back - he will be too expensive.
Andrews will sign a bargain deal, he is a Patriot for life, his wife and he are part of the whole community. The Patriots are only waiting to sign him due to his absence last year - IMO. We can save the $$ on Thuney and get a 3rd round pick or offset for signing someone else BB has in mind.
I am sure a smoother transfer of coaching duties from Dante also helped with the franchise tag decision on Thuney to stabilize the OL for a year when coaching was changing.