If you have an attacker that can obtain the token within 30min, it is reasonable to assume they might obtain the token immediately, and use it immediately too.

JWT expiration protects against situations where the token is stored (or made to be stored) somewhere improper and later used, not being pilfered during proper use.

As the article argues, it doesn't even protect against a malicious user using stale credentials to wreak havoc, such as a disgruntled employee that had access to the precious admin panel being fired.

If the JWT is saved as a cookie, you can delete the cookie and the user’s browser is safely logged out. The threat model is that a user or third-party could intercept and reuse the JWT after logout. Sure. But then a malicious actor could re-use a JWT before you logout from the app also, which is a much larger risk. Malicious browser extensions for example could hide that they’re making clicks or taking actions in tabs just as they hide ads from you. Don’t get me wrong, extensions are sandboxed, but… any sandbox can be broken. In the end, whether or not your JWT was revoked at logout doesn’t affect the risk of malicious activity all that much as long as cookies behave the way they should. And as long as your JWT has appropriate expiry timestamps.