It's had a lingering presence amongst fandom dating back to the Silver Age through Imaginary Stories and eventually into post-crisis when Diana was crushing on Clark, but to be fair, that was only because Steve Trevor had been taken off the table by Perez who foolishly thought the character made Diana "weak", and it took thirty years for Steve to be brought back to prominence.
In those thirty years, DC pushed Diana and Clark's bond hard, even after Clark moved on and married Lois, Diana was still trying to muscle in (which I don't think was the right move at all, as it just made Diana look like a potential homewrecker). It's not hard to see that, when the time came to restore and to evolve the traditional ways, they had to diminish the level of Diana's feelings towards Clark so as to ensure she dare not get in the way of his happiness with Lois and Jon. You can't give Clark and Diana the same kind of flirtatious friendship anymore with a family involved, it just looks ugly. Alternate Universes are your only option