From a financial point of view the answer is because you’re not paying for it

Teams is bundled with Office 365 to steal marketshare from other companies like Discord who charge a bit more and are a stand alone service. It’s why Salesforce bought Slack.

CFOs at Fortune 500 companies want to be efficient with their spending so they won’t buy an extra license if their existing bundle is “good enough”

Teams is “good enough” so Microsoft doesn’t invest in it as much as other more profitable areas