Caring makes people weak.
He is a man of power and power is the only thing that counts. Play the game, move the pieces, watch the outcome, begin anew.
No family, no wife, no kids, no close friends to distract him or to give others an advantage over him. The resulting loneliness was a prize he’d been willing to pay.
His only weakness was the love for his little brother. The only one who could ever touch his heart, from the moment he had been born and his miniature fingers gripped Mycroft’s for the first time.
When he first started working for the government, he saw that his feelings for Sherlock were a flaw and he tried to get rid of them, tried to push him away. He managed to destroy the close relationship they had and he let Sherlock fall when he desperately needed someone to catch him.
He realised soon enough that he couldn’t escape his emotions and tried to repair the damage, but Sherlock – memory like an elephant – never forgave him.
So now he worries and cares for Sherlock from a distance. And is grateful that John is there to spare his brother the loneliness he is living.
Because now that he is older he feels it. It doesn't seem worth it any more. And it hurts badly.