The page represents the consensus view among academics who study genocide, including the leading Israeli academics who study the subject.
Wikipedia has policies around what constitutes a reliable source, and academics who study a particular subject and publish in peer-reviewed journals are generally considered among the highest-quality sources. In this case, they nearly unanimously agree that what Israel has been doing in Gaza is a genocide.
It took Wikipedia a long time to come to this determination. At first, academics were divided, but as time went on and Israel's actions became ever more extreme, opinions shifted and nearly all academics in the field started calling it a genocide. That caused Wikipedia to start calling it a genocide. There was a very long process of discussion and debate on the talk page of the article leading up to this change, centered on an evaluation of the sources.
Jimmy Wales has now come along and essentially ordered the Wikipedia community to change the article. He's effectively ordering them to disregard the usual "reliable source" guidelines and instead represent a view that he personally feels is neutral.
The thing is that Wikipedia editors don't necessarily respect Jimmy Wales that much, and they generally don't think he has the right to dictate what any particular article should or should not say. Wikipedia has been around for more than 20 years. It has well established rules and a community of editors. Jimmy Wales is just the guy who originally set it up, but he's not necessarily an expert on anything.
> There was a very long process of discussion and debate on the talk page
Could you link to it? It's seems key to the issue. Many refer to it - including in the discussion with Wales - but nobody seems to link to, refer to, or analyse it.
This is the discussion that led to the opening sentence of the article being changed: https://en.wikipedia.org/wiki/Talk:Gaza_genocide/Archive_12#...
As you can see, it wasn't just a few editors saying, "lol, let's just say it's a genocide." Hundreds of people weighed in on the proposal. They looked at lists of recent sources.
There were previous discussions like this that came to a different conclusion. But as more and more sources started calling it a genocide, Wikipedia editors eventually decided the opening sentence had to be changed.