I'm pretty sure this didn't use to need an extension, at some point I definitely had my new tab just set to "about:blank" which accomplished the same thing.
But Google decided that's not actually what you wanted to do and removed that feature.
Funnily enough the blank page extension was made by a Chrome developer, so I assume there were some team internal tensions and those who wanted to keep that feature were overridden..
And Google is probably right - for most people, if all of a sudden their new tab page was just a blank screen they'd assume something was broken. It was pretty easy to change that setting without knowing what it meant.
Installing an extension is a much more obvious process - it has a description and screenshots showing exactly what it does, so nobody should be surprised.
Both chrome and Firefox have been shifting to moving any behaviour that could appear as "broken" out of their settings and into extensions. I wouldn't assume tension in the team because a chrome Dev built the extension, more likely just normal process.
Don't you worry -- Mozilla isn't immune from this. They removed this feature on Firefox for iOS which is super annoying. You can type in new tab page but it's not allowed to be about:blank.
Yay installing an empty HTML page on my server just to have basic functionality.
I mean, they could surely work around that right? Use something like an empty data:text/html page instead of about:blank if there really is some sort of iOS restriction.
There are so many useful use-cases. Like... imagine you want to try out a html snippet, without creating an html-file. "Clearing" the default new-tab-page takes some seconds before you can insert your own stuff via the dev tools.
Remote work environment involving screen sharing during calls/meetings. As a Firefox user I don't need an extension for this, but I set the new tab page to blank.
I have a separate work profile on my machine, but still, the default page of most frequent / most recent / most whatever pages is too unpredictable for me (i.e. I am not 100% sure how it works and don't want to devote time to understand it completely). I have rarely used it anyway, CTRL+T then typing a letter or two is way faster than trying to spot the relevant box and click it (separate URL / search bars help here as well).
A nice image is cool and all, but it may be too distracting, and then there's the problem of unpredictability again: it comes from a 3rd party (extension developer) using another 3rd party (Bing in this case) to fetch the image. Bing being known for its excellence in the less worksafe areas and all... I won't take my chances :)