Read it the following way: We have a reason to do it but we don't want to tell you so instead we will tell you a little bit of righteously-sounding bullshit so that most of sheep base is satisfied. Yes, that's "sheep", because you are not our customers, our customers are those companies we sell your information and your focus to.
Or maybe, there are people who would believe it, but they have an account already. And most simple do not care. They read, they have to create an account to get the content, so they do create an account.
I hate this idea that, as a society, companies are permitted to bullshit people and the onus is on the consumers to be able to parse the borderline lies from full truths. My wife used to work closely with people with moderate mental illness - you wouldn't believe the predatory scams, advertisements and "offers" they fell for.
Edit: I guess it wasn't sufficiently clear, the second sentence here is not my own personal opinion.
Distortion-fields aren't so powerful that they cause people with integrity to discount critical thinking. If someone can be sold on this with hand-waving, they probably lacked integrity or critical thinking from the start.
Nonsense explanation means just that users' interests were not factored in the decision.
FWIW, here in Sweden I can still look at feeds without being logged in.
As someone who's been writing integration (not nefarious!) scrapers for years, this is crap. Email accounts are free, VPNs and captcha solvers are dirt-cheap and at the end of the day, if they screw up the web version too much, the mobile apps are even easier to turn into scrapers as they usually use some kind of JSON API.
They did this for the same reason as Reddit and Facebook: - it's harder to make ad profiles for anonymous users - new users is a metric that investors love - psychological trick (I can't remember what that specific phenomenon is called) to turn lurkers into posters
I have two reactions to this:
1. I absolutely HATE this kind of arrogance from companies.
2. I don't believe them. I think it's far more likely they are doing this to juice their metrics, rather than honestly thinking that taking away options will make everyone like them more.