because every villain is the hero of his own story
There were times when he had risen to power and they had come to find him and take it away, always speechifying about justice for whatever group were their underdog of the week. But at least he got to see them.
And there were times when they got too self-assured and he had gone to find them and show them he still had the fight in him. And even when it ended badly, which it generally did, at least he got to see them.
The Master couldn't remember when last he and the Doctor had been "on top of the world" (funny Earth-English expression, that) at the same time... unless he took the alien phrase literally.
That year. At the time, it was the longest the two of them had been in proximity since they were inseparable schoolmates nearly a millennium ago.
The Doctor had been, again literally, his captive audience. All he'd wanted was their admiration... for them to look down at his new and improved version of their favourite world, and agree that it was good. Even if they'd only said it with their eyes, it would have been enough. But they spoke nothing, and their eyes were dull with loss.
When he went to find them and hauled them around the ship (by the tie, by the arm, or in that handy wheelchair) they'd always shy away from his direct touch. Did they fear he'd torture them telepathically as well? Not a bad idea. Were they so disgusted by his brutality towards their favourite aliens that they wouldn't deign to share headspace with him? As if they'd never wiped out entire sentient species before (and better, more advanced ones than mere humans)! He usually let them get away with avoiding the link, so they wouldn't read how much he longed for their response.
But sometimes, when his confidence was real and his shielding was strong, he'd grab them by the head so hard he could feel not just their mind but their skull protesting, and mentally command them (it wasn't begging -- not if no one else could hear his desperation) to talk to him. Their silence then hurt so much worse; it smelt of the Doctor's disdain.
And even knowing that the Master would abuse the humans more, as punishment by proxy... still that great Defender of the Earth said nothing.
And then he'd tire of them (it wasn't giving up -- not if no one could read his despair) and throw them back in their cage... And he'd go take out his frustration on Lucy. It's not like she was a real person.
(So, he'd underestimated her a tiny bit. Perhaps everyone had.)
and when he was bested
not by his Doctor, as it should be
but by that Terran Doctor Martha Jones
(another one he'd underestimated)
and when the Doctor arose in power
and when the Master fell in terror
then, then they had the gall to talk
and talk and talk
and of course in their triumph they forgave him
what he'd done to others for them (always for them)
because 'i forgive you'
is code for 'you have sinned'
then, he needed to hurt them
break their spirit as they'd broken his strength
from Lucy's revenge, he improvised his own
and it worked
the keening of their mind as he breathed his last
it was so beautiful
and at least he got to see them.