RasulAllah صلى الله عليه و سلم said,

مَنْ مَاتَ وَلَيْسَ فِي عُنُقِهِ بَيْعَةٌ مَاتَ مِيتَةً جَاهِلِيَّةً

"And whosoever dies without having a Bay'ah upon his neck he dies the death of Jahiliyyah." [Muslim]
People use this hadeeth to use the Bay'ah as a style to make pledge to the current rulers because they are in authority, or heads of a group or a Tareekah. This is due to a failure to understand that there is a difference between the Linguistic and Shar'i (Legal) meaning of the word Bay'ah.
Linguistically, the word Bay'ah (Pledge) is a commitment or a pact. The Noble Qur'an mentions the Bay'ah of Ridwan بيعة الرضوان or Bay'ah of the Tree بيعة الشجرة. Also, the Pledge of Women بيعة النساء, the First Pledge of Aqabah, the Pledge of War بيعة الحرب, the Second Pledge of Aqabah. Each of these references has a certain Kareena (Contextualization) which gives the word Pledge its meaning. Allah (SWT) said,

يأَيُّهَا النَّبِىُّ إِذَا جَآءَكَ الْمُؤْمِنَـتُ يُبَايِعْنَكَ عَلَى أَن لاَّ يُشْرِكْنَ بِاللَّهِ شَيْئاً

"O Prophet! When the believing women come to you pledging to you that they will not associate anything with Allah" [Surah Al-Mumtahina 60:12]

لَّقَدْ رَضِيَ اللَّهُ عَنِ الْمُؤْمِنِينَ إِذْ يُبَايِعُونَكَ تَحْتَ الشَّجَرَةِ

"Indeed, Allah was pleased with the believers when they gave the pledge to you under the tree." [Surah Al-Fatah 48:18]
Both these examples refer to making a "Pact with you" which is يعاهدونك. upon a commitment to Islam and not to establish a Ruler ruling by Islam.
Seerah of Ibn Hisham also mentions another example, referring to the Ansar.

بايعنا رسول الله صلى الله عليه وسلم بيعة الحرب... ومنها أنّا نأخذه على مصيبة الأموال، وقتل الأشراف.

We pledged the Pledge of War, that we would accept the loss of wealth and the slaughter of the nobles."
This refers to the Bay'ah made by the Aws and Khazraj to RasulAllah SAW for Nussrah to establish the state in Madinah, and to sacrifice all in this matter.

However, if the word Bay'ah is mentioned without any Kareena (Contextualization), then it has a specific Shar'i meaning, which is a specific methodology to appoint a Khaleefah. It is a Pledge of Offer and Acceptance and the subject is authority for ruling by Islam over the Umah. The one who gives a Pledge to an Ameer of a group or a Tareekah will not absolve himself of this duty.