I find it amazing the PFBB is held up as the gold standard for starter sets. IMHO, that distinction goes to the 81 and 83 Basic boxes.
While the '83 Red Box was great (I can't comment on the '81 version), it's also 30 years old. As such, it's of limited use as an example, because a lot of people simply haven't been gaming that long.
Besides, actually, the contents of the PF set are actually
better than the '83 Red Box - 5 levels instead of 3, 12 character options instead of 7, plus a battle map, pawns, and pregenerated characters.
The one big weakness of the PF set (and, in fairness, it is a pretty big one) is the omission of the AoO rules, which mean that combat has a rather different feel in the BB versus the 'real' game. I'm not sure how they could have done that better, but, yes, it's an issue.
They were actual games, with supporting adventures and expansions.
The PF Beginner Box is an actual game, and has
supporting materials. Indeed, it has additional adventures and a DM kit available
for free.
B3 Palace of the Silver Princess
B4 The Lost City
B5 Horror on the Hill
Quite a few more, but hopefully this is a decent enough selection to contrast it against a Beginner Box that was a single-use game from a company that had no intentions of supporting it as anything but a gateway to a similar but not-quite-the-same game.
Again, there are supporting materials available, both from Paizo (including free adventures) and also from third-party publishers. And where the Red Box had the B-series of adventures, the Pathfinder set can be used with any low level Pathfinder adventure, of which there are many (the user may need stats for the additional spells, feats, monsters, and magic items... but those are also
available online for free).
Beyond that, yes, it would be good if Paizo would support the Beginner Box with its own dedicated line of adventures and, even better, an equivalent of the Expert Box. But, unfortunately, the market just isn't there - it really does seem that people either advance to the 'real' game in short order or they just walk away.