When does BCE begin and why then? It seems arbitrary and possibly prejudicial or anti-prejudicial. Also confusing to the reader who may be culturally acquainted with BC and AD.
BCE is used specifically to allow the speaker/writer/reader to reference the same commonly-used time scale and reference base whilst avoiding any explicit appearance of acceptance or endorsement of Christian religious doctrine, especially where such would be considered sacrilegious in some other religious traditions.
This useage has been in routine employ in the non-denominational writings of religious scholars and in some of the academic world for a very long time.
In fact, the expression has been traced back to 1615, when it first appeared in a book by Johannes Kepler as the Latin usage vulgaris aerae, and to 1635 in English as "Vulgar Era". The term "Common Era" can be found in English as early as 1708, and became more widely used in the mid-19th century by Jewish academics.
In the later 20th century, the use of CE and BCE was popularized in academic and scientific publications, and more generally by authors and publishers wishing to emphasize secularism or sensitivity to non-Christians, by not explicitly referencing Jesus as "Christ" and Dominus ("Lord") through use of the abbreviation "AD".