*Some

Is the keyword, GMO purposes can be vast, and not all are just for pesticides or non-fertility.

Some are even used to be more pest resistant so it can be less reliant on pesticides.

Store all the food they need (until they can fuck) when they could eat in their juvenile form.

Having other areas of your field with better pay/conditions/benefits can put more pressure on even non union places. Since there will be better contions elsewhere, there will be an expectation of a level of compensation/more people looking at those union places, requiring even the non union locations to at least increase something to compete for talent.