You need to add
pal_layer.placement = QgsPalLayerSettings.Line as it seems Line feature needs placement property to be defined.
pal_layer = QgsPalLayerSettings()
pal_layer.fieldName = 'facilityid'
pal_layer.enabled = True
pal_layer.placement = QgsPalLayerSettings.Line
labels = QgsVectorLayerSimpleLabeling(pal_layer)
Below are the available options:
Arranges candidates in a circle around a point (or centroid of a polygon). Applies to point or polygon layers only.
Arranges candidates over a point (or centroid of a polygon), or at a preset offset from the point. Applies to point or polygon layers only.
Arranges candidates parallel to a generalised line representing the feature or parallel to a polygon's perimeter. Applies to line or polygon layers only.
Arranges candidates following the curvature of a line feature. Applies to line layers only.
Arranges horizontal candidates scattered throughout a polygon feature. Applies to polygon layers only.
Arranges candidates scattered throughout a polygon feature. Candidates are rotated to respect the polygon's orientation. Applies to polygon layers only.
Candidates are placed in predefined positions around a point. Preference is given to positions with greatest cartographic appeal, e.g., top right, bottom right, etc. Applies to point layers only.