I see most Chinese Malaysians that took up Singapore Citizenship
because they are married to Singaporeans plus they have children/a
child born in Singapore. And for those single Chinese Malaysians
who had PR status and already served NS, both their parents are
here in Singapore so they might as well become Singaporeans. And
for the first generation Malaysians who had PR status before, well,
they had their own personal reasons to become Singaporeans.
However, I think one of the reason that hid deep within their
hearts that made them to become Singaporeans was because they knew
Singapore majority is Chinese and is good for their personal
development.