What have 9/11 victims' families said after accused entered into plea bargain? Why will they not get death sentence?

Alleged principal architect of the al Qaeda attacks on the Twin Towers, and two alleged co-conspirators, Walid Muhammad Salih Mubarak Bin Attash and Mustafa Ahmed Adam al Hawsawi, have been languishing in the US military prison of Guantanamo on the coast of Cuba since 2003.