I already see a problem, with this question that starts with the
title.
Not all Malaysians, are ethnic Malays. Although yes, ethnic
Malays do form a 60% majority of Malaysia's population. The other
40% of Malaysia's population are ethnic Indians, Han Chinese and
some indegenous groups. Malaysia's population isn't really that
diverse.
Indonesia on the other hand, is one of Southeast Asia's most
diverse countries. You are to understand that, "Indonesian" is not
an ethnicity but rather a nationality. There are MANY ethnic groups
in Indonesia. And guess what? Malays are one of them. Indonesians
are also ethnic Malays, but not all Indonesians are Malays. Sure,
there are a lot of Malays in Indonesia and most of Indonesian
culture is based off of Malay culture. But ethnic Malays are only
about 10-30% of Indonesia's population. They mostly live in Borneo,
Sulawesi (formerly "Celebes"), Sumatra's western coasts and they
form a minority population in Java.
So if, only 30% of Indonesians are ethnic Malays at the most;
then what are the ethnic groups that make up Indonesia? Most of
Indonesia's population are Javanese, and they make up about 50-60%
of Indonesia's population. Javanese people are not Malays, although
they closely related to ethnic Malays. Javanese people also have
their own language, the Javanese language along with Indonesian;
the national language of Indonesia. Malays and Javanese do look a
like, because they share the Austronesian origin.