I would've roughly agreed if Jiggs was indeed cut during Brawl's development - it's worth noting that Hungrybox didn't start to become well-known until 2008 / 2009. I'm not going to pretend that HBox is a primary factor in this context - he isn't - but he's heavily identified with Puff for a good reason.
Now though, it's a bit of a different story mostly because Jigglypuff has a whole lot more history behind it and has already survived previous close calls. As such it's arguably more difficult to cut it now (barring situations where they have much less time than they had back in Brawl). Also, Jigglypuff continues to be prominently featured in ads, such as
this one a couple months ago.
It has a sizeable casual playerbase -
27th most used online according to ultimategamedata, slightly behind Samus and a bit ahead of Kirby in terms of usage (Puff is 10th out of the 12 64 characters - Fox is actually the least used amongst the Original 12). Quite a lot of casual players choose Jigglypuff not just because it is appealing (although that is a primary factor) but also because it has a strong aerial game + some flashy stuff like Drill -> Rest. On the more Serious Business side,
BassMage and
Arika are notable Puff players in Ultimate.
It's difficult to judge how much of an impact history actually has - while we do know it plays a part (otherwise Sakurai would've been more open to just reworking characters from the ground up) we don't know if it's going to be a big factor going into Smash 6. Still though, I wouldn't be surprised if the sheer inertia that has been built up at this point helps Jigglypuff from now on.