For a presentation that's traditionally meant to be the biggest each year, E3 is in an awkward position on a Feb-Jun-Sep cadence, since it covers the shortest period of time that's usually the slowest in terms of new releases, meaning going big at E3 often entails showing off the holiday game or next holiday's game that they'll end up covering again down the line. With E3 finally dead, Nintendo has more flexibility to reorient their marketing schedule, and it makes sense to apportion out the June Direct.
September Directs have been a staple of the Switch era, though, ostensibly due to their proximity to TGS. Would Nintendo really shift those up to August? It would be a relatively minor change, but those have stuck around even in recent years.