To prevent unexpected and major changes to LTSC, all inbox (or "Store") apps are removed from the release. Store apps are constantly being updated, and over the long lifetime of a LTSC release, that's bad thing. LTSC sacrifices newer functionality for longer-term stability.
Therefore you get the legacy versions of apps like Notepad.exe, MsPaint.exe and SnippingTool.exe.
The UWP app framework is supported on LTSC, so you can install Store or Store apps but that's your decision to make.