Intel reacts to pressure from AMD. Right now AMD is pushing against Intel with Ryzen 3 CPUs and higher.
So then, what reason does Intel have to make Pentiums quad core? Right now, if you are buying a CPU in the Pentium price range, AMD doesn't have anything competitive. Right now I could buy a Coffee Lake Pentium for $65 and the least expensive Ryzen is $99, a completely different price point.
Intel could offer quad core Pentiums to undercut AMD's Ryzen 3s, but then Intel would be undercutting their own i3s too.