Short answer:Japan had little interest before the late 19th century- and even then Sakhalin was remote, and Japan had other territorial ambitions that were a higher priority.

Discussion:

Earlier in the 19th century, there was some informal presence on Sakhalin by both Japan and Russia, but this was remote territory for both nations-- its only later in the century that you get mechanisms of government that far in the hinterland. Hokkaido itself is frontier territory for Japan: Sapporo is a very new city, founded in 1876-- so Sakhalin is yet more remote. Russia's first settlers in Sakhalin are a penal colony, the indigenous Ainu population is treated very badly, and is perhaps %20 of the small population by later in the century.

In the Treaty of St Petersburg [1875] the Japanese ceded all control over Sakhalin to the Russians, in exchange for the Russians ceding sovereignty over the Kuril Islands (this was a measure of Japanese weakness in the face of Russian strength).

In the Russo-Japanese War [1904-5] the Japanese invaded Sakhalin. In the Treaty of Portsmouth brokered by the United States which ended that war, the Japanese kept the southern half of Sakhalin, the dividing line between Russian and Japanese parts being the 50th parallel.

In the Second World War, the Japanese and Soviets remained at peace until 1945 -- neither needed another front. The Yalta Declaration held that the Soviet Union would enter the war against Japan three months after German surrender-- in August 1945, Soviet armies seized southern Sakhalin and the Kuril Islands; they'd been promised southern Sakhalin in the Yalta agreement.

Finally, Sakhalin wasn't any kind of historical territorial priority for the Japanese. They weren't much interested in empty places-- they'd known of Hokkaido for a very long time, and basically had little interest beyond Hakodate. Given that Sakhalin is quite similar to Hokkaido in its resources, only colder and yet more remote, Japanese interest was even more attenuated. Japanese imperialism historically had been oriented towards Korea -- note for example Toyotomi Hideyoshi's invasion in the 16th century. In the early 20th century, Korea, Manchuria and China were all far more interesting to Japan than Sakhalin-- indeed so was Taiwan.

Sources

THE INSTITUTION OF RUSSIA'S SAKHALIN POLICY, FROM 1868 TO 1875

THE LEGACY OF THE SOVIET OFFENSIVES OF AUGUST 1945

The Northern Territories in Japanese-Soviet Relations

THE TERRITORIAL DISPUTE BETWEEN MOSCOW AND TOKYO: A HISTORICAL PERSPECTIVE

Pioneer Economy of Sakhalin Island [1939]

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