Community ManagerDeronBraun I am not speaking for Microsoft but would like to share experience from several projects in this regard.
"Why/how is it a customer cannot run Office ProPlus on LTSC but can run any other edition."
LTSC releases, this will include Windows Server starting from 2025 are not suitable for Office use. The point is that the codebase (Windows Core OS) is fixed by design and does not match with the needs of SaaS which Office (Apps for Enterprise) is.
Even though LTSC 2019 (1809) is a good LTSC release, other than LTSC 2015 (1507) and LTSC 2016 (1607) which had a lot of issues that #wontfix by design I would greatly advice the customer not to choose LTSC for anything other than MSFT states LTSC should be used for.
With the current knowledge of Office Support Matrix, I would even make clear to refrain from ideas running Office (Apps for Enterprise) on Server 2016/2019, as this would mean a restructuration in less than 5 years.
This is not only to disencourage the customer. The will have to subordinate to to have upgrades every 18 to 30 months. If planned carefully once, I can certainly say this can be a big benefit, too for compliance and security.
Using Windows 10 LTSC should reflect that modern hardware might not be supported, when released after time of release of LTSC, or that even OEMs like DELL will not support Windows LTSC with drivers and security fixes at a point.
Ultimately the 10 year support timeframe (which is 5 years paid extended support) is not a good enough deal to legitimate all the drawbacks you will be facing. It is also not possible to switch from LTSC to SAC or vice versa without fully reinstalling the OS, and bascially not planned to in place upgrade from any LTSC to a later LTSC, which would raise the deployment costs significantly.
I often read about people, also home users, plea to use LTSC to have lesser issues and lesser upgrade needs, but that point is mostly invalid on the long term.
See my link about about the compatibility and support matrix: https://query.prod.cms.rt.microsoft.com/cms/api/am/binary/RE4tOEc
