Here's one reason that adults have illogical beliefs:

During childhood, each person acquires particular beliefs about life. Some of those beliefs are inaccurate. Some of those beliefs conflict with each other.

All beliefs in adults must be consistent with beliefs acquired during childhood.

Beliefs in adults that are consistent with inaccurate beliefs acquired during childhood are likely to be inaccurate.

If a person's beliefs during their adult life change, then that person acquired beliefs during childhood consistent with both sets of beliefs held as an adult.

The beliefs acquired during childhood do not change during adult life.

The change process described on this website removes inaccurate beliefs acquired during childhood.