The yield per hectare of palm oil is 5 times higher than the next most productive edible oil crop (rapeseed).

Note that there is nothing wrong with palm oil itself, it's just that the cheapest way to produce edible oil on Earth, is to grow palm oil trees in a tropical climate. Replace palm oil with another vegetable oil, and the effect on deforestation will be even worse, as we would need even more land to grow the replacement. Even Greenpeace is not calling for a boycott or palm oil.

Presumably 1 ha of tropical forrest > 1 ha of temperate-climate forrest, that is if the replacing crop would be a temperate-climate one.

>What did we do 10/20/30 years ago before it was ubiquitous?

We used partially hydrogenated vegetable oils: aka trans fat. It's a texture/spreadability thing for junk food and baking. Use of trans fats accelerated after the 1980's declared saturated fats harmful and they took its place. It didn't work out so well and now palm oil is phased in to replace it.

Population growth is probably somewhat of a factor. Oil palms produce so much oil that they are one of the most productive food crops as well as leading the pack in oil production -- competing with rice or potatoes in calories per acre. As another poster noted, the largest consumer is India where it's used for cooking.