"Why? Who are their direct competitors delivering the same sort...

"Why? Who are their direct competitors delivering the same sort product in IT engineering?"

In terms of the PCB market which is the bulk of Altium's revenue, KiCAD is a rising competitor in the small/medium business space, and it's FREE. As in completely free, open source.
It has gotten insanely better and more competitive in recent years since CERN took over it's development.
So now there is a serious free choice for the small or even medium level level company or contract PCB designer.
Sure, it doesn't have the depth of professional level features that Altium has, but ultimately when it comes to PCB design and layout, these features are just productivity enhancers, and not a showstopper that stops a designer from using the tool to design a product.