It's not just disallowing imported code, it's disallowing all dynamic code. This prohibits, for example, Greasemonkey/VioletMonkey/Tampermonkey, or any kind of extension that has dynamic behaviors.
It's a prime example of draconian security absolutism, and it's vile & detestable & anti-human. Enforcing this not just on their store, but on the web & extensions in general, is an outrage.
That seems a liiittle hyperbolic. In any case, power user tools like Tampermonkey will seemingly be supported. Whether that be through special exceptions or new APIs remains unclear. Personally I'd like to see integration with Local Overrides.
Preventing any kind of dynamic agency from growing on the web is one of the most severe threats to user-agency I can imagine. It's a direct strike at one of the most core distinctions that makes the web different from everything else. I really believe strongly that the web will advance once we start making more adaptive scripts/extensions, scripts that can gain & accrue capabilities, and this directly prevents advance.
V2 extensions are no longer allowed but there's still no progress or path for Tampermonkey to even experiment with.
declarativeNetRequest still doesn't have capabilities sufficient to reimplement uBlock Origin functionality. Besides that, it puts the power to decide which blocking capabilities are even possible strictly in Google's hands.
Given that, it's quite clear it's a malicious move to take control away from the user.
If you mean disallowing importing remote code, that's to prevent malware from hiding in Chrome extensions until after being published.
[1] https://developer.chrome.com/docs/extensions/reference/decla...
[2] https://blog.chromium.org/2019/06/web-request-and-declarativ...