For many Health IT systems, systolic and diastolic bp measures are tracked in a database separately. For all other observations, there is not a case where there is a requirement to remap from the way the data is tracked in the database to the FHIR resource recording it. This creates a tremendous challenge when mapping data from Health IT systems to FHIR resources, as the mapping is not one to one for the way the system tracks it. While it is entirely technically feasible to "make it work", such implementation changes result in more complex code, with greater difficulty to maintain. One could argue the semantics of "blood pressure measurement", and I would not argue the semantics with you. It's not a question of semantics, it is a question of ease of use and maintenance.

You've essentially applied a V3-like requirement to the FHIR US-core profile specification. And yes, I have watched providers take my blood pressure measure, and only record the ONE measure they cared about in my chart.