Logistics.

I answer this question once or twice a week (nothing against you asking it — you couldn't have known if you didn't search), and what it boils down to is that Russian America was governed between 1799 and 1867 by the Russian American Company, a private enterprise focused on profit above all else.

Its focus on profit meant it had a strong incentive to keep the number of Russians in America low. Every Russian in America was someone it either had to pay wages to or upkeep for (in the case of soldiers and Orthodox priests/monks/missionaries).

Before the RAC monopoly (and even through the 20-year period of the first charter and Baranof's governance), anyone who attempted larger-scale colonization was foiled by a lack of supplies, ships wrecked by storms, or Native opposition. During the first decade of the 19th century, for example, there was a five-year period when no Russian ships visited America.

Until the 1860s, Russia's Pacific ambitions were hampered by a lack of facilities on its Pacific coast and the sheer distance between European Russia and that coast. Okhotsk was the primary Pacific port until the site of Vladivostok was taken from China.

American and British traders supplied the Russians instead, carrying manufactured goods and foods to Alaska, hunters south to California and furs to China. While this brought profit to the RAC, it was not a basis for large-scale colonization.