Where the personalization / customization of specific UI elements/components is occurring in modern applications

Facebook has progressively released the customizable avatars stickers for its users around the world Messenger app (apparently to compete with the Bitmojis), which follows the trend for instant messaging apps to allow users to customize this aspect of the user experience.

But the more recent and probably more curious feature is Microsoft Teams allowing users to customize their video chat background (custom background feature), which doesn't really have a practical use (except if you don't like to show people where you are actually having the meeting).

Rather than focusing on customization of core user interface features like the layout and themes or colours of the application (e.g. to help with night mode or accessibility), we are seeing more examples of personalization of user interfaces and interactions on the smaller aspects of the application.

My question is, are there any specific reasons or trends that is pointing to companies focusing on the customization of minor user interface elements rather than continuing to developing a user experience that is customizable across the whole applications (like the layout or features that are accessible)? Are these more likely to be filled in by third party designers and developers?