Mitre serves two primary roles. First, they're a technical advocate for various US military and intelligence agencies, representing their interests at conferences and in committees and helping them shape policy and practices in that advisory role. As such, Mitre is granted levels of trust and access to agency materiel that no contractor has. As such, Mitre is not supposed to take work that might compete directly with the financial interests of contractors and thus must engage only in activities that are non-competitive: advising or coordinating, rather than building systems.
The second role Mitre plays is as a FFRDC (Federally Funded R&D Center), a long term R&D facility dedicated to one government agency, directly serving their interests (as Jet Propulsion Labs serves NASA). In Mitre's case, the clients are the FAA, Homeland Security and cybersecurity, or the US military's (C3I) Command Control Communications and Intelligence interests (mostly run by the army).
An FFRDC maintains staff with various specialized technical subject matter skills that serve the needs and plans of the agency, who often act on behalf of the agency with the internal access and authority equal to that of a government employee. But this close relationship with the government often extends to the non-FFRDC parts of Mitre too.
https://www.mitre.org/centers/we-operate-ffrdcs
Advancement at Mitre is unlike the typical contractor, where you manage increasingly large parts of contracts. Mitre benefits most when you establish an ever closer relationship with the government agency and people therein. The higher the governmant authority you report to, the more valuable you become within Mitre.
Publishing papers and reports to and on behalf of your agency makes you (and your team) more visible and useful to that customer, increasing the agency's desire to engage more Mitre services and rely on them for more uses. Mitre tech staff (usu software developers) often build and show lots of demos before agency managers (and generals) that prototype capabilities they want to explore and advance.