I’ve always been skeptical on the apparently acritical adoption of infinite scrolling, and finally I found some studies on the topic:

Long, endless pages are good for time-killing activities because users are in the mindset for serendipitous exploration and discovery.

Endless scrolling is not recommended for goal-oriented finding tasks, such as those requiring people to locate specific content or compare options. 
— Hoa Loranger (2014) Infinite Scrolling is Not for Every Website

This confirmed my experience on the subject. Going for infinite scrolling is surely an improvement in terms of load time and smoothness of the experience, but it’s often applied because it’s “nice” instead than having a real reason behind it. Sometimes it’s even done ignoring to implement basic technical requirements such as changing the URL with pagination as you scroll and unloading the past content so it won’t kill a mobile device by consuming too much memory.

But it’s not just about technology, it’s also because an infinite scroll create the perception of infinite data (would you like to think of something infinite when you’re looking for something?) and makes you lose any implicit frame of reference (where am I now?).

Pages create implicit frames of reference: they support our visual memory by creating cues: “it was one of the first pages”, “it was at the top of the page”, etc.

Also, reaching the end of a page requires a decision: infinite scrolling takes that decision away, so you just keep scrolling, and that’s why it works for flat content streams, but sometimes that decision is actually good, like for example when looking at search results: if it’s not on the first page well, maybe change your query text? That’s the kind of thinking that it triggers, and a good design can create very useful decision moments that go beyond simple pagination, for example showing different product categories on an e-commerce, or similar products, or variations: these are all navigation alternatives that can happen only when infinite scrolling is not present.

Note that in theory you could show a different “navigation” element in the middle of an infinite scroll, thus creating that moment of choice, but then you are adding complexity by introducing a further choice: should I continue scrolling or navigate away?

In short, do infinite scrolling if:

1. It’s flat, non-hierarchical content.
2. There’s a consumption goal.
3. There’s no need to keep the frame of reference.
4. There’s no further action or decision after scrolling.

Don’t do infinite scrolling if:

1. It’s structured, multi-faceted content.
2. There’s a finding goal.
3. Frame of reference is useful.
4. The end of page can trigger a useful decision moment.

Thanks Mel Choyce for the link.