The point of the sun and moon wasn't to fight evil general or to light Middle-earth for the sake of light. There was not much reason to think it would have helped a great deal. It was mostly about an attempt to restrain Morgoth, since they did not dare go to war against him again, in fear of the damage it would cause. As well another new reason. There were answers in the writing immediately before and after what was quoted in the question.
These things the Valar did, recalling in their twilight the darkness of the lands of Arda; and they resolved now to illuminate Middle-earth and with light to hinder the deeds of Melkor.
...and Manwe knew also that the hour of the coming of Men was drawn nigh. And it is said indeed that even as the Valar made war upon Melkor for the sake of the Quendi, so now for that time they forbore for the sake of the Hildor, the Aftercomers, the younger Children of Iluvatar. For so grievous had been the hurts of Middle-earth in the war upon Utumno that the Valar feared lest even worse should now befall; whereas the Hildor should be mortal, and weaker than the Quendi to withstand fear and tumult. Moreover it was not revealed to Manwe where the beginning of Men should be, north, south or east. Therefore the Valar sent forth light, but made strong the land of their dwelling.
"Of the Sun and Moon and the Hiding of Valinor" - The Silmarillion
It was about fighting Morgoth without going to war, and a hope of making the awakening of humans a little safer. Outside of those reasons they probably did not see a need to light Middle-earth (and were probably cautious about doing so after Morgoth knocked down their first attempt, with the pillars).