The HoloLens 1 was always considered somewhat of a prototype device, and today Microsoft made this somewhat more clear, announcing in the support documentation for the device that it will not receive any further OS updates.
The release notes state:
HoloLens (1st gen) is entering Long Term Servicing (LTS) state. Future updates will focus on issue and security fixes, while maintaining feature parity with the Windows 10 October 2018 release for HoloLens (also known as RS5).
This means features introduced in Windows 10 May 2019 Update onwards will no longer be coming to the device, and will instead only be available on the HoloLens 2.
While developers who purchased the $3500 headset may be disappointed, it is likely only a small number of users are affected, as last we heard little more than 50,000 of the headsets have been sold.
Via the WC