I remember hearing that some of the writers didn’t like the Newt character so many of the scripts had her dying. Still wish those characters got better endings even if they died in 3.

Mostly just timing. Originally they didn't think they could get Sigourney Weaver back. She was too famous by then and hadn't been interested in making Aliens until they gave her a fat paycheck. Fox assumed she was done with the franchise, which is why early versions of Alien 3 (including the first treatments by Neuromancer author William Gibson) either didn't feature Ripley at all, or in a tiny cameo.

But, eventually Weaver relented and agreed to be in the film, but by then, Michael Biehn (Hicks) was booked solid for 2 years, including in the timeframe where they wanted film Alien 3 with Weaver. Hicks was the central character in the William Gibson Alien III (and does his own voice alongside Lance Henriksen in the fairly-good audio drama adaptation released a few years back). But his character wasn't considered essential to Fox, so they went with a script that didn't utilize Hicks, which was essentially a mashup of ideas from previous iterations, mostly Vincent Ward's version, only moved from a weird wooden planet (yeah, who knows) to a prison, and Ward's monks turned into a religious cult of prisoners. I'm assuming they just decided it was too hard to get from Aliens to an Alien 3 set on a prison planet without just killing off Newt and Hicks.