In previous games it was made quite obvious that those in positions of power and control had the means to find, repair, and maintain such reactors. This explains why the Enclave and Brotherhood of Steel are pretty much the only main factions that are able to have working Power Armor, usable transportation, and expansive bases such as the Oil Rig, Raven Rock, and the Citadel for some examples. Even the second most technologically powerful forces in the Fallout lore such as the New California Republic and Mr. House don't have such an expansive network of technological resources; House comes close but even at his best he can only reasonably take care of New Vegas and nothing else. hardly anyone else had the technological capacity and ability to enforce their power over the use of working Pre-War nuclear technology. And even if someone did manage to get a reactor running, the Enclave or Brotherhood of Steel would be quick to come in and swipe it away, as per dictated by their lore.

But no, running power armor is easy enough for a raider to do and powering it with fusion cores is easy enough to accomplish when every major seller has multiple fusion cores on them.