I see people here have run to the "rescue" :P
I'll give my opinion on what might be wrong:
a) topic
b) tagging
c) copyrighted images
d) lack of engagement
e) use of bidding bots
f) heavy curators' workload that might lead to "missing" posts
Don't forget, all this work is done manually by human beings. If, in any case, anyone feels "neglected" or "undervalued" or if you think another author deserves more attention, we'd be happy to hear you in the complaints room of our discord server (mentors and curators are there for all of you) :)
Ohhhhhhhhhhhhhhhhh! You are picking the topics for steemstem? Alright my bad for even asking!
I am one of the many curators on board ;)
Posts are voted after discussion and team work :)