I don't think skeuomorphic is what you think it is. From wikipedia: (1)

> A skeuomorph (/ˈskjuːəˌmɔːrf, ˈskjuːoʊ-/) is a derivative object that retains nonfunctional ornamental design cues (attributes) from structures that were inherent to the original. Examples include pottery embellished with imitation rivets reminiscent of similar pots made of metal and a software calendar that imitates the appearance of binding on a paper desk calendar.

A digital skeuomorph GUI emulates real-world objects and attributes to provide a recognizable and sensible frame of reference to an end-user. For instance, a digital calculator app visually resembles a real-life calculator, the use of the "play" and "rewind" buttons in a media player, the "folder" or "document" icons in a file manager, the use of an envelope to represent an e-mail,...

Now, literally none of that has to do with the style used to represent those symbols. You could draw a "flat" envelope icon using only black and white colors in the famous Ligne Clair style and it would still be skeuomorphic design. (2)

Apple didn't invent skeuomorphic design when it developed and released the iPhone. That's a misconception. Skeuomorphic design dates back to the 60's and 70's when companies such as Xerox built the first GUI's. Douglas Engelbart's "Mother of All Demos" given in 1968 arguably laid the foundations which would be incorporated by Apple and Microsoft in their products (3)

... and then there's the Web. Which is literally a connected mesh of distinct pages implementing the ideas of hypertext. At one point, people started to treat static Web pages as indepedent functional user interfaces. Because there are particular business benefits to doing that over building native applications (i.e. the whole SaaS thing, cutting out distribution of code, etc.).

And so, here we are in this hot mess where you have people re-inventing the wheel building web applications, SPA's, using all kinds of nuts 'n bolts frontend frameworks while browser vendors and organizations like the W3 are trying to catch up with API's. Meanwhile, static websites are still very much a thing and designers and (frontend) developers are doing that too. There are as many visual languages as there are people building things to put on the Web.

And so, everything ends up bleeding into one another, influencing one another,... Some things coalesce and you see visual elements being picked up and repeated all over the place. Like, that time when Bootstrap was all the rage and it was like half the Web consisted of hero images and jumbotrons. Or that regrettable, yet luckily short-lived trend of using a background video in your header image. At this point, it seems like bright colors and "flat-drawn" "Kurzgesagt" style are in vogue. To be sure, this will pass too in due time.

To me, it seems strange to lament that the colors or the loss of skeuomorphs are turning an interface "infantile". It's not. That's just barking up the wrong tree.

What makes an interface infantile is designing and implementing a language without considering the end user. It's one thing to consider the individual affordances of an interface - colors, fonts, skeuomorph elements - it's another thing to consider the interface as a whole and concluding that it's just badly implemented. Much like a joke you have to explain before your audience gets it.

Many designers lose themselves in the former, arguing the merits and downsides of "flat design" without giving the latter enough thought.

(1) https://en.wikipedia.org/wiki/Skeuomorph
(2) https://en.wikipedia.org/wiki/Ligne_claire
(3) https://en.wikipedia.org/wiki/The_Mother_of_All_Demos