Vladivostok is barely the closest populated Russian area.

Its a major base of operations for the Russian Pacific fleet.

Russia has the technologies and infrastructure for efficient resource extraction under extreme conditions

Now, sure. And France has the technology and infrastructure to extract resources from the Mississippi delta region now. But the Alaska purchase was in 1867. Russians were still trying to secure territory on their own continent during this time. Repeated wars with Japan, the Ottomans, and with domestic insurgencies plagued the country through the 19th century.

And Alaska was already being filibustered by western colonialists as far back as the early 1800s, necessitating a Treaty (the Russo-American Treaty of 1824) to settle an ongoing dispute over territory (The Oregon Boundary Dispute) that Russians had little capacity or real interest in prosecuting. Much like with the Louisiana Purchase, this was a token transfer intended to get some kind of compensation to relinquish a claim the Russians were poised to lose one way or another.