Because this is a democrazy and that Mullah MP has the freedumb of speech/expression whatever to not sing Vande Mataram, because there isn't a law against such behavior presently.
But there can be.
View attachment 64898
If it was up to the Mullah MPs they wouldn't have sung the national anthem also, but perhaps there is a law preventing such treacherous behavior.
The momin sees Mazhab and Desh in a false equivalence perspective, you have to "choose" one over the other, and being the saccha, 5 baar Namaz Musulmans they are, it is always Mazhab Alhamdulilah.
Then again according to their book they are all supposed to live under the rule of a Caliph doing ummah-chummah, so what does this jahil kuffar know ¯\_(ツ)_/¯