While Armenians bore the brunt of the Ottoman brutality, there were Assyrian, Syriac and Orthodox Greek massacares/genocides too but for some reason these are much less known and rarely talked about.
The main reason is that the Armenian people do a lot more lobby work in that regard. They also have their own country, unlike the Syriac-speaking people (that includes "Assyrians"). That gives the cause way more backbone.
I suppose you're right. There are many more Armenians around than there are Assyrians/Chaldeans. In general though, this area has important histories that are seemingly ignored.