I'm not saying I'm against hard content, but is it worth developer's time to create super hard content.
This is a bell curve. If you ever learn statistics, this is used constantly
Making content that is for the farther right (like SD+1 or SD+2), more hardcore, group worth their effort? Content that 16 to 2% of player can will enjoy? Or is it, as a developer, better to make content for more left, less hardcore, group. Like at the SD-1 spot would be probably ideal, for profit. 84% of the population could handle that.
In short, hardcore content is not really cost effective from a development stand point. Resources to to appease 2 to 16% of the player base is hardly worth it.
EDIT: This is just a sample bell curve. Just used to make a point.