Probably because you spam posted your site.
"spam"
Well according to the rules of reddit (which you agreed to when you signed up for an account with them) this is not allowed.
I am not 100% sure if this would be considered "spam" or not, but it was certainly against the rules and you were trying to manipulate the system.
Rules are selectively enforced
I would disagree with this. I would say that when the mods/admins of any given site are made aware of the fact that rules are being broken that such rules will be enforced in those instances. I do agree that there may be some instances when rules are broken but the mods/admins do not know of such rules are being broken, and as such cannot enforce such rules.
One example of this is ban evading on this forum. I would assume that many people break the rules around ban evading on this forum, and that such ban evading goes unnoticed by the mods/admins. However as soon as such users admit to breaking such rules, their alternate accounts will promptly be banned for ban evading