One of the members of his core team said “Rajinikanth started backtracking since early 2020.Whenever there was an ‘outside influence,for a day or two, he would move towards politics like this announcement & return to oscillation soon after;he was always looking for an exit route” https://twitter.com/rajinikanth/status/1334388604404002816

Though Rajinikanth had reservations about accommodating BJP in his alliance (read minority votes), final alliance planned was in line with 2014 Lok Sabha alliance in TN.
Rajinikanth + BJP + PMK + DMDK + TMC + Puthiyathamilagan etc.
(PMK + TMC + PT werent keen to come without BJP)

On Oct 29, he released a statement about his health+Covid.
The member said “At this time,he almost prepared an exit’ statement, sensing this,’outside influence’ convinced him not to. Surveys were cited.Few ‘political meetings’ took place in the end of Nov which resulted in Dec 3”