Why was Avraham the only person that, according to tradition, was tested by God 10 times?
According to Kabbalah in Zohar, just like Avraham was tested with 10 trials, so is everyone. That means every person has 10 major tests in his lifetime.
Rav Moshe Feinstein in his Darash Moshe (Genesis 25:27, ArtScroll Judaica Classics, page 48):
Avraham had the ten trials, and Yitzchak allowed himself to be bound on the Altar; and yet, it is Yaakov who is the "select one of the Patriarchs," and whose face is engraved on the Throne of Glory. What is special about "יעקב איש תם יושב אוהלים," Yaakov, the wholesome one who dwelled in tents (Bereishit 25:27), that Avraham and Yitzchak, who withstood many trials, didn't have?
Rav Moshe answered that Yaakov dedicated himself "constantly and exclusively to Torah and mitzvos, which is greater than any trial.