As
@dirkmoses has shown, the majority of states deliberately narrowed the legal definition of genocide to preserve their ability to use genocidal levels of violence against national groups under a security or military logic. For instance, to crush insurrections by targeting entire populations. The UN Convention of 1948 was thus “depoliticized.”
I wonder how many people have actually read Lemkin's chapter on genocide. If you read it, you'll find that he wanted to use the word in a way that was much broader than either its popular or its legal meaning. Lemkin fought for his broad meaning after World War II, but by the time of the Genocide Convention a much narrower meaning - a subset of the very worst of what Lemkin had in mind - became the meaning that prevailed.
The thing is, you can't have it both ways. What makes genocide so horrifying is that it's a (serious) effort at physically exterminating an entire people, or at least the entirety of them who are in your power. Contrary to what Lemkin had in mind - and even Lemkin admitted there were conceptual problems with this - it doesn't mean cultural assimilation of the people of a nation you've conquered, such as efforts by the Nazis to "Germanify" Poland.
We can praise Lemkin for actually coining the word, but no one now uses it the way he originally wanted, and that's a good thing.
As a result of the wrangling in the late 1940s, we have a perfectly good word that stands for the crime of crimes: an attempt at physically exterminating the people of an ethnic, racial, religious, or national group, as Hitler attempted (with considerable success) with the Jews of Europe. It doesn't mean being the more powerful participant in an asymmetrical war; it doesn't mean breaching IHL; it doesn't even mean large-scale war crimes. It means something more specific, the very worst of the worst of international crimes, with the Holocaust as the paradigm.
The concomitant of all this is that the word, with its suggestion of ultimate evil, should not be thrown around loosely.
If we want to say that someone has gone to war in circumstances that will inevitably lead to a lot of civilian deaths, we can say that (and we're entitled to be critical of it if we think there was an alternative). If we think someone has committed war crimes such as aerial bombardment deliberately targeting civilians (as happened on both sides during World War II), we can say that. There are lots of things we can say to make very serious accusations connected with war. But genocide is something beyond any of that, and its connection to the supreme evil of the Holocaust in the popular understanding should not be taken lightly.
When someone makes an accusation of genocide that clearly doesn't match either the popular understanding or the legal definition, you know you're dealing with someone who is either a propagandist who is deliberately lying or someone who is simply ignorant of what the term means. I assume that it's usually the latter - there are many well-intentioned people who are not knowledgeable about any of this and can be swayed by others who seem like experts - but there's also plenty of the former around.