I think it’s branding and momentum, actually.
There’s no indication in the title of the remake that it is, in fact, a remake. Since the first lust quest has the most attention it’s the one that continues gathering attention and people will try that one first because it’s the one they see first. And because of the description of Cannie that leaves no indication of a sequel, people will just kind of sit and wait for an update to Cannie.
I think if you labeled the sequel AS Lust Quest 2 or like, Lust Quest: Definitive Edition that included both the remake and Ice, it’d get a lot more people to play it, along with linking to it in the original.