The celebration of the Bengali New Year—Pohela Boishakh—is a cultural festival exclusively rooted in Bengali heritage. It is for Bengalis alone to decide how they wish to observe it. If they choose not to celebrate it at all, that too is entirely their right.
How one chooses to celebrate is a personal matter. The standards or customs by which it is done are to be set by the individual, not by others standing by with arbitrary yardsticks of cultural correctness.
Those in Bangladesh who trace their heritage to pro-Pakistani Bihari or Punjabi communities are welcome to observe their own traditions, such as Vaisakhi or Baisakhi, in any way they deem appropriate. Just as Bengalis expect their cultural expressions to be respected, others deserve the same autonomy, without external interference or judgement.
For those who do not identify with any ethnic or geographical heritage, or who find little relevance in such identities, or whose community has no historical connection to the Boishakh celebration—there is, quite simply, no obligation to take part. And if the festival holds no personal or cultural significance to them, then neither excitement nor opinion is required.
Let cultural celebration be what it truly is—an expression of identity, not an imposition.