The President's Rule was destined, which Kumaraswamy wanted to avoid. He and Deve Gowda had pushed BJP to the wall to extract the Maximum concession. They had hoped that BJP would succumb as there was no hope for BJP in an early election, especially after the Local Poll debacle for that party. But the Push was a little too much for the BJP to bear.
Devegowda had also predicted, or rather tried his best, that Kumaraswamy would continue as a Care-Taker CM. But Congress was very much alive and was waiting for the moment to strike. No sooner Kumaraswamy resigned, than the Governor chose to go for the President's Rule. That was the best option for the Congress and it used the opportunity to its advantage.
But it is better for Karnataka that Kumaraswamy did not become the Care Taker. He would have taken care of himself at the expense of Karnataka in all these period.