'Shipping' seems to be derived from relation-ship-ing; and I first heard the term in relation to the on-going Harry Potter series - when online 'fans' would spend vast amounts of effort and time in discussion the nature and possible future of relationships between Harry and Hermione, Harry and Cho, Ron and Hermione, Snape and Lily and so on.
Fan Fiction rapidly began to burgeon with shipping narratives; including what used to be termed 'slash' fiction (derived from an earlier era of Kirk/ (the slash punctuation mark) Spock stories - i.e. 'shipping' Kirk and Spock).
I first came across slash around the time of Peter Jackson's Lord of the Rings movies - when there seemed to be a lot of slash Fan Fiction products (some parody, some serious, some pornographic).
Shipping, in a general sense (including slash) is now very prevalent in fandom - almost to the point of dominating some of the most popular TV shows, movie franchises and teen novels. Indeed, it seems that 'shippers' (those who do the shipping, write the fictions and discuss it endlessly) are setting the agenda and framing the discourse.
I regard shipping as mostly an appalling corruption and degradation of fiction; and I suspect the motivations of those involved. In particular, I deplore the trend to re-frame all friendship in sexual (or potentially sexual - will they-won't they?- or dishonestly-denied sexual) terms.
(The Netflix TV series of Shadowhunters, and the books themselves, as I understand, are serial practitioners of this trope.)
This began in the sixties - for example William Ready's early biographical and critical book about Tolkien suggested the Inklings was a kind-of homosexual grouping. But now it appears that the subversion is simply taken from granted; and that the friendships of Frodo and Sam, Merry and Pippin, Legolas and Gimli are simply assumed to be slash-until-proven-otherwise.
Likewise the fandoms of all traditionalist recent narratives, from Harry Potter, through Strange and Norrell, to Star Trek and My Little Pony to whatever latest blockbuster TV series - are seen through the lens of shipping - as mere fodder for sexual speculation and fantasy.
And since the modern sexual arena is so debased by superficiality, fickleness, selfishness and exploitativeness, this has the effects of dragging a lot of potentially elevating and ennobling and inspiring work down to the level of salacious sniggering.
As I say, I don't think this is a random occurrence - indeed, I strongly suspect that there is a degree of conspiracy, funding, planning and purpose behind (and manipulating) this systematic debasement of The Good - wherever it is found.
The mass of fans are, mostly, victims; but in return for short term stimulation they are colluding in trivialising and destroying exactly what they find most valuable about the things they love.