There are rules in the Quraan which aren't said before Quraan so why people left without knowing something is wrong for thousands of years.
The shari'ah has evolved with the humans and it can be noticed through out human history. I am not sure of the verses which report the following:
- When the story of the sons of Aadam(a.s.) is mentioned, that both of them did a Qurbani but, the fire from the sky consumed only one, which indicated that only the one consumed by fire had been accepted.
- In Surah Yusuf, in the end, the brothers of Yusuf(a.s.) performed sajda in front of him, which in our shari'ah is totally haram.
So, if you see the instances it clearly suggests that as the horizons of human mind broadened and the maturity developed, many things were removed from the Shari'ah and some new were introduced.
With the coming of last messenger i.e. Prophet Muhammed (s.a.w.) the human mind has evolved and can perform rational thinking and it doesn't need any miracles to understand things.
Also, Allah(s.w.t.) clearly says in Quran, that I have perfected the religion for you today, which means that w.r.t. to the human in today's time the religion was not perfect.
Hope it answered your question.