This article is pretty embarrassing - it misses so much nuance, particularly around multi-step sign in, and magic links. I don't think the author has actually thought through the user need here. A few examples:
(1) Multi-step sign in flows – as noted in other comments here – are incredibly useful for any product which supports multiple authentication methods. The email is used to point the user in the right direction, versus putting the cognitive load on them to know their own authentication type, or making them enter their password multiple times.
(2) Magic links are incredibly useful in a few places: an example would be something you use infrequently (and thus won't remember your password and/or have a cookie clear between sessions), something where you're typically authed via SSO (same deal – you won't remember your password, etc.), or where you need to sign in via mobile. Mobile sign in, in particular, is really frustrating with special characters. Most users remember that they hit shift+5, they don't remember that that translates to "%". However, they almost ALWAYS have an email client with an active session. Magic link emails are a great way to help that user get into the product with minimal pain.
Generally, I'd assume that most companies have put a lot of thought into this (Google, Slack, etc.), and they don't deviate for "fun", they support these patterns because there's an established user need.
Source: experience as a PM on sign in flows across a number of products.