Why was Russia unable to secure its territory in the north of the American continent?

In my opinion, there were several reasons for this:

1. Joining the already huge country of overseas possessions would entail the need to keep troops and bureaucrats there, which was very costly;

2. Too far remoteness of these territories from the center, which would interfere with effective communication;

3. The government was experiencing a financial deficit, especially in Russia itself, reforms were long overdue for a long time, which required financial costs and efforts.

Perhaps, by selling its American possessions, the Russian Empire wanted to improve relations with the United States, and to replenish the treasury.