Why not though? Public Holidays are already 'events' in people's calendars in the fact they are important and don't happen all the time, anchoring around them, especially having regular fixtures on set dates, helps feed that perception that it is a match worth attending regardless of where on the ladder team's are. (Good Friday & Kings Birthday are great examples of that this year where both teams were in the lower half of the ladder yet still drew above average crowds).
Of course that's not to say that we shouldn't be trying other initiatives to help improve the importance of a match, like Beanies for Brain Cancer round, but we also have to be realistic that it's very hard to make something that happens 10+ times a year at the same venue an 'event' and also appreciate that round based concepts also don't resonate with teams equally (Beanies for Brain Cancer has traditionally worked well for Newcastle, but not other markets, WIL round has traditionally been big for Penrith, but not as big for other clubs).