Why not? I asked Gstaff what happened to those "Meaty and big expansion sized DLCs" and this is what he said
"This is something we thought you guys would enjoy. Admittedly, it’s a smaller add-on (made by a significantly smaller team). We’re still keen on doing “big and meaty” content, too"
i have posted this in several threads,Just want you guys to know that this is just something small we get meanwhile we wait for something big

And i think we'll get something bigger then dawnguard. Think of dawnguard like the knights of the nine of skyrim,but bigger.