From "do no evil", to "we don't really care".
Google Talk is another of those fine examples of how corporations turn away from something what works and is desired, toward something fitting their corporate strategy. Google has been "ill" with the blind following of the blind corporate "strategy" for quite some time now. Talk is not the first victim - and not the last. It's not that the Hangouts can be somehow monetized, compared to the Talk.
The web-based Hangouts are simply not the same as the standalone, OS-integrated client.
I am sort of stuck with the Google Talk because it mostly(*) works and because it is (was(**)) the best Google Mail notifier.
(*) When Google rolled out the Hangouts, they have broke and never fixed the file transfers in the Talk. Needless to say that the Hangouts did never support the file transfers at all.
(**) Well, Google has managed to break that too: since about one year, Talk still can properly detect the availability of new messages, but it fails to clear the "unread mail" indicator after the messages were read. Same version for the past 5+ years, meaning Google broke something on the server side.
All that leads me to believe that the breakage was deliberate. As if Google simply can't tolerate when people actually find their services useful...