I usually get at least one or two dragons. Last STW I got none so I feel your pain. I had to spend gold on some extra spins to get the dragons I did. Otherwise I would have had just the duplicate Franken.
Feels like my "luck" ran out the higher level I got and the more dragons Ive acquired. Its probably coded in to give higher level players less of a chance. I'm at 150 and have 430+ unique dragons. Definitely feels that way to me at least. Always had some luck at lower levels.
They want you spending your hard earned gold. Higher level players even more so. Gotta give lower players a bone here and there to keep them playing.