I don't work for Adobe and I have no inside knowledge on this. So it leaves me free to speculate.
Why is server use forbidden? Let's look at an idea. We have an office with 100 people who want to make PDFs.
Well, they can buy 100 licenses and each person can do this. Or, perhaps the software could go on a server. Instead, only one license is sold.
For the software maker this is not a good outcome. So licenses are written to forbid this kind of usage.
In general as a developer you need to be aware that every piece of software you intend to use on a server must have its licensing terms carefully checked. Failing to do this can be a very expensive mistake. For example, some companies have a license allowing them to charge for each separate human who uses the software. Companies have faced bills of millions of dollars for putting desktop software on a server.
Even server software needs carefully checking. For instance some have limits on users or on network use - perhaps limiting to the local network. And the terms of no-cost software must also be checked, because free does not mean unrestricted.