[Inziladun]

First, the Meneltarma remaining above water after the Downfall was only a belief among the Dúnedain, never proven.

Second, the peak itself was described as being very steep. The apex was only accessible via a winding road that almost certainly was destroyed.

At the top, it was said to have been "somewhat flattened and depressed, and could contain a great multitude" (UT A Description of Númenor), but that doesn't translate to being livable. They would have needed suitable land for farming, and mountain peaks don't typically fit that bill.