At this moment, nobody has a majority. Even munyiddin is scared of no confidence vote in parliament as before this, he got a one or two seat majority. Losing one or two votes is easy.
Theresa May in UK needed the Ulster unionist to maintain her majority in parliament.
Current Boris johnson does not need them. So he is not bothered about a open Irish border after brexit.
Similarly, muhyiddin needed sarawak party, umno, parti islam for backing. They can ask whatever they want and he will give it to them.