now() default values are all showing same timestamp
That is expected and documented behaviour:
From the manual:
Since these functions return the start time of the current transaction, their values do not change during the transaction. This is considered a feature: the intent is to allow a single transaction to have a consistent notion of the "current" time, so that multiple modifications within the same transaction bear the same time stamp.
If you want something that changes each time you run a statement, you need to use statement_timestamp() or even clock_timestamp() (again see the description in the manual)
now() and current_timestamp are STABLE functions returning the point in time when the transaction started as timestamptz.
Consider one of the other options PostgreSQL offers, in particular statement_timestamp(). The manual:
statement_timestamp()returns the start time of the current statement (more specifically, the time of receipt of the latest command message from the client)