You must be a bit dumb, then.
Both Malaysians and Singaporeans can travel to Europe visa free for 90 days (out of 180 days), 90 days no visa required, as you put it.
Nationals from the poorer countries you mentioned cannot, and thus need visas.
Some countries allow Thais to enter for 90 days without a visa, such as Brazil, and thus Brazilians can enter Thailand for 90 days without a visa too.
Who'd a thunk it could work like that, eh.