They didn't. They extended the life for eight more years and still make a profit from Sun hardware sales today. If you looked at the alternatives: IBM or stay independent then those were not going to end well. Oracle gave Sun life for eight more years.
Oracle was the best think to happen to Sun in 2010. You have to understand the market dynamics at UNIX vendors at that point. Look around. There are zero UNIX server vendors any more.
Mostly they have a sustaining team, just like Oracle. Solaris is still supported but purely in a payed sustaining mode for legacy customers until 2034.