This is likely due to GCP Tags used instead of Labels which are the AWS and Azure equivalent of "tags".

Google Terminology:

Google terminology uses both terms of Label and Tag.  

• Label: Labels are a lightweight way to group together resources that are related or associated with each other. For example, a common practice is to label resources that are intended for production, staging, or development separately, so you can easily search for resources that belong to each development stage when necessary. Your labels might say vmrole:webserver, environment:production, location:west, and so on. You always add labels as key/value pairs.  
  Source: https://cloud.google.com/compute/docs/labeling-resources
  Important note: GCP's term Label is equivalent to AWS and Azure' term Tags.
  
  
• Tags: A tag is simply a character string added to a tags field in a resource, such as Compute Engine virtual machine (VM) instances or instance templates. A tag is not a separate resource, so you cannot create it separately. All resources with that string are considered to have that tag. Tags enable you to make firewall rules and routes applicable to specific VM instances.
  Source: https://cloud.google.com/vpc/docs/add-remove-network-tags

Tags are intended to enable a user to configure network setting and are not intended to categorize your infrastructure.  Tags are not currently provided in the BigQuery Billing Artifact, which is where CloudHealth receives your cost data.  Accordingly, Tags are not available in the OLAP reports, as these are derived from BigQuery.