At the beginning of the novel, Justice Wargrave is thinking of all the times he has seen Soldier Island in the news. First, there was the fact that an American millionaire had bought it. Since this story was set in England, that might make the news. Then a beautiful modern home was built on the island, and the home was featured in the news. The third wife of the millionaire was killed in a boating accident on the island, and that was in the news. After that the millionaire wanted to sell it, so various advertisements of the home and island had been in the papers. Finally came a statement that a Mr. Owens had bought it.
Gossip also made the papers concerning the island and the beautiful home. It was rumored that a Hollywood film star, Miss Gabrielle Turl, bought it. Another rumor was that it was sold to royalty. Mr Merryweather was said to have bought it for a honeymoon, and it was rumored to have been sold to the Admiralty to carry out some hush-hush experiments for the government/military.
There was definitely a lot of interest in this island, and that is why Justice Wargrave believed that this island was newsworthy.