Why startEvent do not support 'default sequence flow'?

[coolstoneyoung]

All BPMN 2.0 tasks and gateways can have a default sequence flow. But Why startEvent do not support "default sequence flow"?

why not support [default="start-useTask-SB"] as below?

<startEvent id="start" [default="start-useTask-SB"] ></startEvent>    <userTask id="useTask-SB"  default="useTask-SB-useTask-WSYSL"></userTask>    <userTask id="useTask-WSYSL"  default="useTask-WSYSL-useTask-SL"></userTask>    …    <sequenceFlow id="start-useTask-SB" sourceRef="start" targetRef="useTask-SB">      <conditionExpression xsi:type="tFormalExpression"><![CDATA[${nextStep == "SB"}]]></conditionExpression>    </sequenceFlow>    <sequenceFlow id="start-useTask-SL" sourceRef="start" targetRef="useTask-SL">      <conditionExpression xsi:type="tFormalExpression"><![CDATA[${nextStep == "SL"}]]></conditionExpression>    </sequenceFlow>    …‍‍‍‍‍‍‍‍‍‍‍‍‍

Thanks!

[trademak]

Because it's mandated by the BPMN specification that default flow is limited to activity types.

Best regards,