While CarePlan.category:AssessPlan definition is "Type of Plan", the fixed code.value = AssessPlan limits it to Assess-Plan:
<valueCodeableConcept xmlns="http://hl7.org/fhir">
<coding>
<system value="http://hl7.org/fhir/us/core/CodeSystem/careplan-category"/>
<code value="assess-plan"/>
</coding>
</valueCodeableConcept>
IT is unclear why obligation of this slide is set to mandatory, i.e. cardinality (1..1)

Assuming that the "assess-plan" value is based on the USCDI data class "Assessment and Plan of Treatment" - which is defined as:
"Health professional’s conclusions and working assumptions that will guide treatment of the patient." (https://www.healthit.gov/isa/taxonomy/term/581/uscdi-v3)
This definition narrowly casts Care Plan as artefact representing the "assessment" and the "plan of treatment" components of the care planning (which includes health concerns identification, health goals setting, care | management activities planning, implementation and outcome evaluations)

While some "care plans" may be narrowly focused (e.g. in episodic care of acute conditions), many more care plans are complex and support full spectrum of care planning and delivery).
The mandatory slice (cardinality 1..1) appears to compel all implementations to assert that all care plans will be at least of the Assessment and Plan of Treatment type.
This design decision is highly undesirable.
Suggestion:
Relax CarePlan.category:AssessPlan cardinality to 0..1