On Commons, the "Add pages I create and files I upload to my watchlist" preference should be checked by default for consistency with other Wikimedia wikis. There is no particular reason why Commons should be any different.
Change 385818 abandoned by GeoffreyT2000:
Set 'watchcreations' preference to true by default on Commons
Discussion started at https://commons.wikimedia.org/wiki/Commons:Village_pump/Proposals#Watch_creations_by_default.
Note that there could be several reasons for this historical specification:
I see in particular that commons users create a large (ie. very large for @Fae and lot other) number of pages, comparing to articles on other content wikis (except WD). For example, would there be performance problems for watching lists to now become huge by default?