Description and name also do not define a feature. Since OSM is a database, it would be impossible for any automated processing (like map rendering or search) to know that this is a memorial from the name - you would need a human to tell that. The purpose of tags is to unambiguously define this so that it's machine-parsable. Also, both memorial and obelisk tags can be here at the same time, if we choose to represent it that way. But monument is for large structures, while memorials are generally for small ones. There is some overlap, but here it's certainly not a large structure/complex like that. But it has to be something because obelisk by itself does not describe this commemorative purpose.

https://wiki.openstreetmap.org/wiki/Tag:historic%3Dmonument#Warnings - see lines 2 3