Which Sahabi name written in Quran?

There is only one Sahabi whose name is written in the Holy Quran i.e. Zayd ibn Harithah رَضِيَ ٱللَّٰهُ عَنْهُ. Why is only one Sahabi named in the entire Quran?

Who was Zayd ibn Harithah?

Zayd ibn Harithah رَضِيَ ٱللَّٰهُ عَنْهُ was the third person to accept Islam after Khadija رَضِيَ ٱللَّٰهُ عَنْهُ and Ali ibn Talif رَضِيَ ٱللَّٰهُ عَنْهُ.

Zayd ibn Harithah رَضِيَ ٱللَّٰهُ عَنْهُ was a slave gifted to Prophet Muhammad ﷺ by Khadija رَضِيَ ٱللَّٰهُ عَنْهُ. Prophet Muhammad ﷺ freed him from slavery and adopted him as his son.

Zayd ibn Harithah got divorced

Prophet Muhammad ﷺ wanted to set an example of equality and thereby got Zayd ibn Harithah رَضِيَ ٱللَّٰهُ عَنْهُ married to Zaynab bint Jahsh رَضِيَ ٱللَّٰهُ عَنْهُ who belonged to a reputed tribe and was a rich and powerful lady. However, their marriage could not go along and they got divorced.

Adopted sons were treated like real sons

At that time, people of Arab used to take adopted sons as their real sons with the right to inheritance. They were treated like Mahram relations in a way that a real son would not marry an adopted daughter. 

Allah ﷻ wanted to tell the people of Arab that an adopted son is not a real son.

Prophet Muhammad married Zaynab

In order to break the taboo, Prophet Muhammad ﷺ was instructed to marry Zaynab bint Jahsh رَضِيَ ٱللَّٰهُ the ex-wife of Zayd ibn Harithah رَضِيَ ٱللَّٰهُ عَنْهُ.

• فَلَمَّا قَضَىٰ زَيْدٌۭ مِّنْهَا وَطَرًۭا زَوَّجْنَـٰكَهَا.

When Zayd had no longer any need for her, We married her to you in order that there not be upon the believers any discomfort concerning the wives of their adopted sons when they no longer have need of them. – Al-Ahzab 33:37