alertmanager: repeat_interval doesn't work

below is the alertmanager config file

lobal:
  resolve_timeout: 5m
route:
  group_by: ['alertname','cluster','host_area']
  group_wait: 5s
  group_interval: 5m
  repeat_interval: 3h
  receiver: 'sreserver'
  routes:
  - receiver: 'k8s'
    group_by: ['alertname','cluster']
    matchers:
      - cluster =~ ".*-k8s"

  - receiver: 'dbserver'
    group_by: ['alertname','host_area']
    matchers:
      - host_role =~ "dbserver|DBserver"

  - receiver: 'BIserver'
    group_by: ['alertname','host_area']
    matchers:
      - host_role = "BIserver"

  - receiver: 'sreserver'
    group_by: ['alertname','host_area']
    matchers:
      - host_role != "BIserver"
      - host_role !~ "dbserver|DBserver"

receivers:
  - name: 'sreserver'
    webhook_configs:
              - url: "xxxxxxxxxx"

inhibit_rules:
  - source_match:
      severity: 'critical'
    target_match:
      severity: 'warning'
    equal: ['alertname', 'instance']

We use vmalert to examine alert rules and send alerts to Alertmanager…for example ,below is a rule about Mem

- alert: 内存使用率
      expr: instance:node_memory_utilisation:ratio * 100 > 95
      for: 1m
      labels:
        severity: warning
      annotations:
        summary: "内存使用率过高！"
        description: "内存使用大于95%(目前使用:{{$value}}%)"

But the question is : Why I receive alerts with this alertname every 5 minutes? Should’t be 3 hours ?

• Alertmanager version:

alertmanager-0.24.0

• Prometheus version:

prometheus-2.37.6