I think you're the one missing the point a little bit. That's your own insiders perspective. Iltaran's touched upon the truth of things, but let me expand. Most Beluaterran outsiders see/saw the Blood Cult as an influential faction in Enweil. This was helped very much by the actions of Mesh. Indeed, when I actually got one of my characters to Mesh and became ruler there, I was totally unprepared for the strength of feeling on the matter. They hated the Cult.
I'm not disputing that the Blood Cult was powerful/well spread/influential etc. But over a period of years Mesh and others very successfully smeared the Blood Cult. The Blood Cult itself did little to help it's cause. Consider things like founding a theocracy in Athol Margos during an Enweilian campaign in Riombara. Plenty linked the Cult and Enweil together.
You mentioned Fronen, but they don't/didn't really have any strong personalities at all. The Blood Cult might have been active there, but you didn't hear about it or come across any of it. When there was the big Grehk/Fronen war Mesh was moaning about Cultists there but no-one cared as you hardly knew they existed. No-one listened because to most minds, the Cult was already one with Enweil.
It's always been the House of Chenier whose name has been in various states of repute/disrepute as a Cultist throughout Beluaterra. And where has the House of Chenier been active most in Beluaterra? For how long has a Chenier been either General/Ruler of Enweil? In that sense, it's always come across very strongly that the Cult has a big power base in Enweil and that Enweil happily supports Cultists.
You can say what you want, but my Beluaterra char has definitely spent the last four years or so associating the Blood Cult most strongly with Enweil.
I'd bring a few nuances to the interesting points you bring forth.
First, the cultists in Enweil wanted you to hate Enweil. Secondly, many who hated Enweil wanted you to hate the Cult. It's a conflict (factions of) both parties wanted. In the end, before the invasion, the Blood Cult had managed to sway the whole continent into a huge multi-front war, which basically consisted of the anti-cult realms (and their friends) and those more tolerant or supportive of the Cult. And this was done because it was considered that the second faction was stronger, and that so after a long and destructive war, the anti-cult factions would be decimated. It wasn't a lopsided conflict, but the conflict on most fronts was either favorable to us or in a stalemate, so it was calculated that those who win their wars could then be re-directed at tie-breakers on other fronts.
That's why Fronen didn't show up in the debate as much. Their government was much less vocally militant, but for the greater part of the Cult's history, that's where all the elders were concentrated. When the Cultist priests tore down the Republic of Fwuvoghor near the end, most of them were based in Fronen, knowing full well that RoF could not afford to declare war on Fronen (as it would give an excuse for its military to come in) and that therefore they could operate with impunity. If you read up the Cult's RP archives, you'll see most of the radical stuff is from Fronenites. Or mostly everyone other than Enweilians, who were generally rather tame.
And the Athol Margos colony was actually established by the prophet who had, until then, lived in Melhed for a very long time. It was a secession from Melhed, and maintained awkward links with it for the duration of its short life. Really, the Blood Cult in Enweil was just 1 noble for the longest time.
