TIMESTAMP NOT NULL field with explicit_defaults_for_timestamp and NO_ZERO_DATE shouldn't throw error

Given the following server options:

explicit_defaults_for_timestamp

sql_mode=ANSI,NO_ZERO_DATE

and the following table creation code:

create table test (

    a int,

    ts timestamp not null

);

The server throws the following error:

SQL Error (1067): Invalid default value for 'ts'

Why can't we create a table with TIMESTAMP field like a normal data type, where we force the user to specify a value, but without providing a default?

(Remove the part about INSERT statement, since it seems to cause some confusion)