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.
Pentium Gold of the 8th gen are not Ryzen's competitors. They are quite cheaper processors with 2 cores and 4 t. designed for light equipment.
I3 are the competitors of Ryzen 3.
i5 are the competitors of Ryzen 5.
i7 are competitors of Ryzen 7.
The classification is a question of marketing and therefore it is not possible to know if in the ninth generation will have 4 cores. What can be ventured is that they will be the last processors to enter the market.