What makes something an Ikkar, is not How basic of fundamental it is to believe in it. An Ikkar is a concept that is vital to a proper theological structure of Torah. Which is fully dependant on whatever starting point the composer chooses. A self understood system of Jewish studies? Rambam. Where we differ with popular medieval thought? Crescas. Logical deduction? Abarbanel.
This is why we do not find a mention of The Ikkarim in the classical sefarim. Even Rashi never mentions them. He had no need for it.