Sometimes they just make up whole new stories (Bleach) or say fuck it and go their own way (Fullmetal Alchemist). I feel like the more accepted recent approach though is having a mini-series of an arc which has normal pacing (actually even often accelerated pacing cause they only get 12 episodes) and then just putting the show on hold.
And then you have when the anime affects the manga and the manga starts stretching the story out for “content” (feel like this happened with My Hero Academia and Welcome to Demon School! Iruma-kun). If it was a novel that’s being published on a pay by chapter platform you’re just completely fucked because they (generally) follow the Mark Twain model of pay per word so once a story gets popular that shit absolutely gets milked into the ground. If you’re lucky they waited to do the anime until the comic adaption was half done at which point the novel will hopefully be done…
I don’t think that has never not been a thing… Read memoirs/letters from earlier times and you’ll see plenty of it too. The big shift was probably admitting the children don’t yearn for the mines, but we seem to be heading back that way (eta: in the USA anyway I won’t paint other countries with our fuckery lol).