Saturdays were always low frequency on the shuttle - they would run every other hour or every third hour, first flight of the day was later in the morning and last flight of the day was earlier in the evening. Same with Sunday mornings.

I first made elite from a year of heavy US Airways Shuttle flying in the early 2000s and was a frequent user for many years after. The "Shuttle" product has had a long decline (including AA dropping the "Shuttle" marketing and giving LGA-BOS over to JetBlue). It was viewed as a "checklist item" for big corporate accounts in the NY/Boston/DC area, and pre-COVID those markets had a lot of day trippers (many booking day of) which supported high frequency (and high fares), and thus more amenities. Acela ate into some of this (especially in DC, with a 2h45m trip time, versus Boston which is nearly 4 hours), and some of the decline must be fewer day-tripping business travelers.

In its heyday you had a number of features which have been discontinued over the years. Dedicated single class aircraft and "extra sections" have been gone since the early 2000s (full flights in the mornings and evenings, but running very light loads in the middle of the day). You also used to have dedicated gates with workstations, free coffee/newspapers in the gate area, open bar on board, rear deplaning, etc. Some features still exist (e.g. on Delta the "memory schedule," shorter check-in times and free cocktails in Y), but it is largely unrecognizable from the product of 20 years ago.

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