Why does zypper dup require system DVD to get new updates.

Running Tumbleweed and most times when I run zypper dup to get the latest updates, it requires installation of the Tumbleweed DVD to finish.
Latest now will not accept the DVD I have been using all along and aborts.
Why do updates require the original install dvd to update?
Why is it now rejecting the install DVD?

Because your repos still contain an entry for the DVD/USB install media. Use YaST - Software - Software repositories to remove it. Or use

zypper lr -d

to see the repo list, then

sudo zypper rr REPO_INDEX_NO_HERE

Because you have the DVD configured as a repo. Disable or remove that repo (as described already by Knurpht).

Why is it now rejecting the install DVD?

I don’t know. But there may have been a change in how devices are recognized, and it no longer recognizes what you have configured. Or maybe you installed a very long time ago, and there has been a change in repo-format since then.

In any case, once you have removed or disabled that DVD as a repo, you should run

zypper dup

to do a full update. Your system is probably out of date, because it is using the DVD to decide what packages to keep, and your DVD might be seriously out of date.

If you are not sure which repo this is, then post the output from

zypper lr -d

and use a code block for that output.