Why is it that hard to rank up fast from silver up rather than from gold to diamond?

I reached Diamond 2, and with my same deck I havent even earnt the May cardback yet after dozens of matches. Playing Imbue/Herald Rogue. Why is that every opponent I face has the cards to generate massive buffed boards and Im here trying to copy them without any success or just trying to hard remove everything without actual plan and thus losing in the end with an empty deck