Ascension underwent a massive recruitment phase during the introduction of world wonders, and placed the wonder race at the top of their priorities, so that probably gave them a simmer reputation they can't shake. The alliance is too large and diverse to really be lumped together in one category though.
There was a small group in the northwest that rejected the emphasis on wonders. Some of them joined SILK or went their own ways.
The large group in the midwest found themselves at war with the player who had previously been ocean leader to over half of them. It was a declared war, but a cold one. There were both practical and emotional reasons to limit the conflict in this region, so while these players may have appeared simmers in the stats, I can personally attest that many of them were willing and capable of fighting under different circumstances. I wouldn't consider them true simmers.
I've had the least contact with the southern cluster based around 47, but my understanding is that they've been fighting DS all along.
The northeast took on new life after george martin took over. They defeated my attempts to create a second SILK stronghold in the far corner, chased a renegade into and through what was left of event horizon, and basically took control over the whole region.
While understandable, I don't believe the reputation is deserved.