count() is not using index

query is
select count(VMs) FROM default
index on VMs is created
cbq> create index a1 on default(VMs);
{
"request_id": "031c4c4a-e874-485b-ab3c-ee3453f84d11",
"signature": null,
"results": [
],
"status": "success",
"metrics":

{ "elapsedTime": "7.052043s", "executionTime": "7.051605s", "resultCount": 0, "resultSize": 0 }

}

cbq> select * from system:indexes;
{
"request_id": "6c3159fe-5dfc-4a58-b65c-720efa71209b",
"signature":

{ "*": "*" }

,
"results": [
{
"indexes":

{ "id": "a1", "index_key": [ "`VMs`" ], "index_type": "view", "keyspace_id": "default", "name": "a1", "namespace_id": "default", "store_id": "http://172.27.33.45:8091" }

},

cbq> EXPLAIN SELECT count(VMs) FROM default;
{
"request_id": "5909a400-7b1a-4b54-a058-a90ef8b86de9",
"signature": "json",
"results": [
{
"#operator": "Sequence",
"~children": [

{ "#operator": "PrimaryScan", "index": "#primary", "keyspace": "default", "namespace": "default" }

,
{
"#operator": "Parallel",
"~child": {
"#operator": "Sequence",
"~children": [

{ "#operator": "Fetch", "keyspace": "default", "namespace": "default" }

,

{ "#operator": "InitialGroup", "aggregates": [ "count((`default`.`VMs`))" ], "group_keys": [] }

,

{ "#operator": "IntermediateGroup", "aggregates": [ "count((`default`.`VMs`))" ], "group_keys": [] }

]
}
},

{ "#operator": "IntermediateGroup", "aggregates": [ "count((`default`.`VMs`))" ], "group_keys": [] }

,

{ "#operator": "FinalGroup", "aggregates": [ "count((`default`.`VMs`))" ], "group_keys": [] }

,
{
"#operator": "Parallel",
"~child": {
"#operator": "Sequence",
"~children": [
{
"#operator": "InitialProject",
"result_terms": [

{ "expr": "count((`default`.`VMs`))" }

]
},

{ "#operator": "FinalProject" }

]
}
}
]
}
],
"status": "success",
"metrics":

{ "elapsedTime": "2.667ms", "executionTime": "2.351ms", "resultCount": 1, "resultSize": 2611 }

}

cbq>