It is arrogance and seeing what they will get away with.
I was just at WalMart yesterday and noticed that Sims 4 Seasons and Jobs packs are for sale, right along side Sims 3 Seasons and Jobs packs. Too bad Sims 2 and Sims 1 Seasons and Jobs packs aren't for sale, too.
This happens for the same reason we get spam. Because stupid people choose to play the game.
(It wouldn't be so shameful if Sims 4 had actually been an upgrade. But, it clearly wasn't. It was merely a "sell less for more" exercise in shaking down the consumer.)
Crowdfunding, which you pointed out, is probably the best solution. Corporations these days seem to believe they can push
increasingly anti-consumer practices (like six different Nvidia cards with the same name number). Of course, there are traps involved, like vaporware. I had been waiting, for years, for the fanless gaming computer case. It looks like it was a scam. Star Citizen... is that thing ever going to be released? I haven't paid much attention.
We know we can expect bad faith from companies like EA, after things like SimCity 5 ("It really does super-awesome calculations on our servers, really!" — "The game plots are teeny-tiny because that's a feature, not a bug, but the feature is to force-feed you our DLC pack!") and Sims ("If you don't buy Sims 4 you'll never get the privilege of paying for everything a fifth time because we will refuse to sell you Sims 5 muah ha ha!"), let alone other franchises.
We know we can expect bad faith from a lot of game-making corporations (beyond the ordinary baseline level of the corporation, as it is a mechanism based in bad faith) but vetting people trying to do crowdsourced games is also a challenge. People with extremely good faith may not have the track record of releases needed to be taken seriously while others may be poor-quality because they succeeded in the most crooked corporations like EA.
