It isn't. Yes, political control exists and has shaped encyclopedias (it has also shaped Wikipedia). The editorship however mainly has to focus on keeping stuff consistent and meaningful for the reader. You have to have no real involvment with scholarly writing if you think just letting random scholars write whatever they think is important will lead to a good encyclopedia.

To put it more concretely, I've read extensive editorial notes by the editor-in-chief of Encyclopedia of Yugoslavia from 1950s/60s, i.e. a govt project in an authoritarian country - the editor was an avowed Marxist and it was no secret, yet his notes were absolutely leading the project in the right direction, he was insistent on critically revising the inherited nationalist political narratives, pruning lots of rhetorical fluff and nonsense, "saying it like it is". It had its bias (pro-Yugoslavian, pro-communist), and it was pretty clear about it, you know where to expect it if you don't like it, and frankly the critical stance was justified. The second edition from 1980s actually caused controversies because lots of powerful people disliked it interfering with their own nationalist narratives. Even in an authoritarian country you can't keep everything under control. The encyclopedia is to this day a treasure trove of valuable information that the existing Wikipedias of ex-Yugoslavian countries can only lick the balls of (in part because they are or have until recently been managed by illiterate fascists, as is the case for Croatian and Serbian WPs).