The comment you reply to does a good job describing one goal of this usage.
You can see virtue signaling in this behavior, and there may be a part of it, but that is not the only reason it is used and it's dicey to jump to the conclusion that virtue signaling can only be the main goal. The fact that you don't see these others goals or refuse to believe that they may be the main reason does not change the reality of the existence of these goals.
It's like people who are saying "if you say you prefer Linux over Windows, it's only because you are jealous of Windows popularity and want to feel different". Maybe it is, maybe it is not. But they just refuse to even consider that maybe the other person is not acting by jealousy.
> I have NEVER met someone using alternative language like "differently abled" who actually did something substiantial for the community or for a particular person. Almost all cases have a touch of patronisation.
That sentence sounds very strange to me: why on earth someone using alternative language like "differently abled" would suddenly be required to do something that you don't even blink an eye for people who don't use that language?
It feels like the virtue signaling resides in your eyes only: you are seeing someone saying X, you _invent_ that it is because they want to be seen as a knight helping the disabled people, and then you show that there is an incompatibility because they don't really act like a knight helping the disabled people.
But what if people using this language don't do it to be seen as a knight helping the disabled people. Then there is absolutely no incompatibility at all.
The fact that this incompatibility exists is even a clue that maybe this behavior has nothing to do with virtue signaling.
> And as a disabled person, I can tell you, I need nothing of it.
I think that the goal as described by the previous comment has nothing to do with you. The goal is to reshape the way of thinking "there is a hierarchy of 'good situation' with abled people on top" into "there are differences, with sometimes good situation and sometimes bad situation, but it's more complicated than that and simplifying the picture as a simple hierarchy is incorrect". The goal is not to please you, the goal is to avoid having a way of thinking that does not correspond to the reality.
It's the same reason why some people stop saying buzzwords like "artificial intelligence" when referring to a smartish complex algorithm composed of if conditions and no machine learning at all. They are not doing that to be fair to algorithm, they do that because there is a gain for them and for the society to not maintain misconceptions.