Some present only 4 sources of Fiqh: Quran, Sunnah, Ijma, Qiyas.
This presentation actually reflects the position of the people of Kalam.
The position of Ahl as-Sunnah is that there are 5 sources:
The 4 great Imams are unanimous on this.
Why this special place?
The Companions saw the Prophet ﷺ, learned directly from him, and Allah praised them in the Quran.
Their understanding of the texts reflects the direct understanding of the Revelation.