Bangladesh closed the gates after the horse had bolted. they could have won the series if the batsmen had more guts in the 3rd ODI. so sad, that they return to BD empty handed, this teaches them a lesson to never underestimate the guys you have beaten up many times, they should have been smart to find out what the opposition is doing and who they are playing. anyhow, also, they should have found out who the new players were and their strengths.
Zim was playing cricket against SA A and Australia A for a while before the BD tour, so they were well prepared for BD.
Anyhow, hope this is a valuble lesson and they will be better prepared in the next series.