Yeah, but even in SEA, most of the Austronesian languages are in those islands that happen to be both in SEA and in the Pacific Ocean.
The only ones that are spoken in mainland SEA are Cham, Chru, Duano, Haroi, Jakun, Jarai, Orang Kanaq, Orang Seletar, Rade, Roglai, Temuan, and five varieties of Malay. There's also up to six language varieties
plus Urak Lawoi' spoken on islands that are not
in the Pacific. In other words, it's most of Chamic, a bit of Malayic, and Moken. No one seems to be interested in learning any of these languages except Malay, so while it's a handful of languages, I don't think it would be a huge loss, either.