Back in the eighties, batteries weren't yet at the point where they could run a laptop with similar computing power to a desktop. If you wanted that much computing power, you just accepted that your laptop needed to plug into the mains.
Given that, early portables used CRT screens on the order of 5 inch. Hard to read and very heavy.
The Toshiba T3100 released in 1986 used a plasma screen. Much bigger display area, thinner, a better choice all round.
But apparently plasma screens were around more than a decade earlier than that, and 1970s plasma screens don't look deficient in the pictures I've seen of them. So why weren't plasma screens used in laptops earlier than 1986? Or is it that they were and I missed it?