Because as a reader at the time it was getting absurd, and irritating, after Crisis merged the worlds, having heroes who had been active in World War II looking like they'd only aged 15 years in 50 years. They were sort of clogging up the place. The "Ian Karkulls temporal fallout" worked as long as you didn't have to think about it too much (such as when they were on Earth-2), but when they were always around, it got... silly.
They had already tried removing Wildcat, by crippling him in Crisis, allowing Yolanda Montez to take over the roleas a Hispanic, female Wildcat, but she never caught on, and met the same end at the same time as the new black, female Doctor Midnight (who ate least spelled her name properly).
Personally, I'd have let the JSA characters die of old age long ago, but that's just me.