Like others said, <PERSON> would not give his followers power over him. A Unbreakable Vow makes both parties equally responsible. Especially if the Vow was a exchange. (You give me your loyalty and I'll give you fame/fortune/power.) Also the Unbreakable Vow requires another person to bind the two subjects. That is an awful lot of power given to someone over <PERSON>. A Unbreakable Vow is a call for help. That is NOT <PERSON> at all. He would never ask for help. Our one example of the Unbreakable Vow was <PERSON> going to <PERSON> FOR HELP. She feared <PERSON> would not be able to complete his mission.
People either followed <PERSON> because they believed in his ideology or feared for their lives. People would rather try to hide or run than fight <PERSON>. He did not see any of his followers as strong enough to stand a chance in killing him. 950
It's well documented the only person <PERSON> feared was <PERSON>. <PERSON> was the only wizard powerful enough to survive a duel with him. Probably because he had the elder wand. We also do not know if the Unbreakable Vow is still active if one of the people die. Once <PERSON> died then people wouldn't fear instant death renouncing him and not staying loyal.
<PERSON> was also a arrogant leader. He rightfully thought no one would be brave enough to betray him. <PERSON> was a loyal follower all the way up to when he found out <PERSON> was going after <PERSON>. <PERSON> didn't betray <PERSON> out of bravery but out of love of <PERSON> and the fear of losing her. <PERSON> betrayed <PERSON> because he treated <PERSON> so badly. <PERSON> knew he would be dead before <PERSON> found out about his betrayal so he didn't fear his retribution. During his first reign <PERSON> did not foresee that love is more powerful than fear so he never considered it.
Also <PERSON> only brought pure blood wizards and witches in his Death Eater ranks who were closest to him. They either were his schoolmates, other pure bloods from the Sacred 28 list of pure blood families, or proved their uses and loyalty in other ways like <PERSON> being a spy inside Hogwarts. He had a lot more followers but those people and creatures did not have a close connection or any valuable information on <PERSON>. 773