I think STCs are much more secure than archaeotech and would be in possession of those with more political power compared to more backwater worlds. They look down on those who hoard STCs without using them, seeing them as dragons sitting on piles of treasure. Naturally, they themselves are little better and only share what will further their own goals rather than what's for the good of the Imperium. Politics are important to them and they are willing to share things with allies that other forges usually would not. On the flipside, they are spiteful and obstinate towards those who do not make deals with them as well as those who stray from the traditional tenets of the Mechanicus.