Some players of Bangladesh only play for themselves. They don't think about the team. There is also lack of proper bonding between the players. There were some senior players like Shakib, Mushfiqur, Mominul in the squad. Also some experienced players in test format like Shanto, Litton and Miraz. None of them showed responsibility during batting. They were unable to stand in front of Indian magic bowling squad.
Bangladesh players this mindset is having huge troubles for them as they are trying to give individually instead of team if they will try to give as team things can take good changes, and they can achieve better results as well.
Same case happening in current Pakistani cricket team, and they are going down day by day this is important while you are developing a cricketer you need to give him some lessons it's not all about captaincy or individual performance you need to be performed as team which will give you better results, and you will be able to have better performance as well.
In few countries, they are doing things like these from the early days of players career which helps him, and he is able to give best for his team instead of going through for personal records and achievements.
You can always underestimate them in test format. Don't forget to check their
test statistics.
I can see that Bangladesh won at least one test match against all test playing nations except India and South Africa. Any country's stats will look like this in early days of test cricket and I do not have any second opinion about Bangladesh is about to transform from here to more stronger side in near future.