From my vague understanding, it was mostly racially motivated why they were expelled from the Malaysian Federation, or was the issue more nuanced? What was the perception within Singapore/Malaysia at the time, one of reluctance or good-riddance?
It was more of, Singapore was kicked out of the Malaysian Federation due to its pro racial equality and tolerance beliefs and policies, which were against those of the ruling Malayan political party UMNO then (they supported a Malaysian state for where Malays, despite being the majority, are favoured and more superior).
It made economic sense for Singapore to join Malaysia as a federation. Independency was, not really a choice, just something it had to deal with