Because Hal, post-Crisis, was an embarrassing problem for DC to solve. At that time(and I'd include myself back then), there was not the nostalgia for the Silver Age that fills Johns and others. Quite the opposite--MAN OF STEEL was emblematic in its resolute anti-nostalgia.(Lois' snickering reaction to Metallo's name in that is probably the best single distillation of that) Instead, the remnants of the SA--starting with Barry Allen, but a lot of the Crisis was bent on targeting them particularly(consider: we start with Earth-3)--were dated embarrassments inappropriate to the modern and dark 80s.
So Hal had the bad luck to have not died in the Crisis. So they had to darken him. That's when we got alkie Hal. This is around then. Consider that so many of these are treating Hal like an embarrassment; this is a reflection of the editors' view, and also the fans. At the time we LIKED watching these perfect and upright characters degraded. You have to understand, back then they were pompous and had been a long time, and the truth is that the retcons of late are more interesting and better-written than the stories they're trying to recall & restore were. NOW we like the traditional versions, but only because we got so sick of the dark.