One thing with dividing timelines is that our subconscious minds are at least some level connected to other timeline selfs. Meaning that you are kinda collective of timeline versions of you. Thats is kinda necessary for differences to be so insignificant.

Like if JFK is in different car in 60s then even that change should have created massive difference in this timeline comparing to other timeline, but if people do have connected minds between timelines then we end up doing same things as other timelines with different timings.

That is just one theory what I have about Mandela Effect.