Islamically neither Sunnis or Shias deserve to go to hell....

[Mystic]

So why do Sunnis and Shias teach the all sects are bound to hell except their own?

For control and power . Also the origin of the core religion.

True said...

1) Hadiths + want of scholars to follow hadiths over Quran where it suits their sectarian bias.
2) Lack of tolerance for creed differences in Islamic culture.
3) For control and power.

Control and power can also be seen as the motivation of 1 and 2.

I would say however this is not a decision they realize. They want to control the masses and have power over them, so as to "guide them"...although inwardly they probably love the position of power and authority and it's high motive as well.

---

I would say it's even more complicated then this.

1) Scholars go their to learn the religion.
2) They already trust the scholars they learn from.
3) The system of knowledge (Imel Rijaal + hadiths) is taken as a proper way to know religion.
4) Contradictions of hadiths with Quran are not realized because of confirmation bias....the same reason why Quran verses and logical problems with them and contradictions aren't realized.
5) They are vested with authority to guide according to the knowledge they have and trusted by the community for knowledge, just as they trusted the scholars themselves.

But in the past...the reason why these hadiths were chosen...was due to intolerance of differences and sectarian bias which was motivated by want to control and manipulate by hadith narrators and hadith collectors and those whom authenticate narrators.