why are some of my steemit posts hidden to low ratings ?

Hello, 

I have made some numerous Sestertius promotion posts here on steemit, but most of them were hidden to low ratings. These posts concerned free sestertius giveaways and are there:

https://steemit.com/sestertius/@tofm2/today-s-free-sestertius-giveaway

https://steemit.com/bitcoin/@tofm2/free-sestertius-giveaway-2017714t123228144z

https://steemit.com/sestertius/@tofm2/free-sestertius-giveaway-now

https://steemit.com/bitcoin/@tofm2/free-sestertius-giveaway-2017712t211759530z

https://steemit.com/bitcoin/@tofm2/simple-photo-2017712t04620136z

Can someone help me understanding this hiding, is it admin caused or what ? In any case, did I break any steemit rules by doing so ?

Best regards.