Context

It is a common usage to call some right-wing conservative movements in Western countries as "reactionary". See Wikipedia:

In ideology, reactionism is a tradition in right-wing politics; the reactionary stance opposes policies for the social transformation of society, whereas conservatives seek to preserve the socio-economic structure and order that exists in the present.

Although it can be meant as a insult, sometimes it is not, and some conservative figures even openly recognize themselves as "reactionary". This is the case of the French far-right political figure Éric Zemmour. He, as a conservative, wants to go back to the old France (if I am not mistaken, the 19th century France). In general though, if I am not mistaken, European conservatives hold high the values of the middle-ages, and want to come back to something near to this period.

Question

If right-wing conservatism is reactionary, why communism (Engels and Marx) and anarcho-communism (Bakunin, Proudhon, Kropotkin) are not seen, by the general public and the medias globally, as reactionary too, in their case extreme-reactionary?

Indeed, they want to go back to the hunter-gatherers kind of society. Marx and Engels coined the notion of "primitive-communism", a state which our society should go back to. The French anarcho-communist Pierre Clastres was also clear about it (Wikipedia):

Some, like Pierre Clastres, consider that the organization of certain traditional non-Western societies (such as the Guayaki) in different parts of the world (the Americas, Africa, Asia, Polynesia), which have lasted for millennia, are at least partly similar to anarcho-communism.

Hypothesis

I would say this is because they stress on something modern: communism emphasizes the preliminary phase of the people dictatorship, and anarcho-communism emphasizes the masses revolutionary struggles. Yet, this is not their project per se, only the means towards their project.