He states it in the article I linked to above. Videos that don't earn money, don't get indexed it seems. The bigger problem is the fact that DTube deletes the majority of videos within a week of posting them as well. But that I read in a separate article, and dont have the link. I stopped posting to DTube for now, they just delete everything I post within a matter of days, not worth it. They need to find a better way to retain videos.
RE: DTube has Alzheimer's disease? -> IPFS Links not working and Blockchain errors