This is no surprise - Microsoft is very specific in terms of how it 'loves' Linux and all of them involve revenue. Microsoft supports Linux in terms of:
1. Allowing users to run Linux apps on their own desktop OS (Windows 10). This helps keep devs on their platform (revenue stream) who might have otherwise moved on.
2. Ensuring Linux VMs run well in their hypervisor. This is purely a play at Azure - MS knows that the majority of Internet platforms use some form of FOSS stack and that isn't changing any time soon. Better to embrace and provide somewhere to host it reliably (i.e. Azure). That makes up half of Azure now, and is steadily increasing. That's at least double the Azure revenue than would be the case without good Linux support.
3. Supporting expensive but niche products like SQL Server on Linux. Once again, new opportunities for revenue in terms of SQL Server licensing.
4. Enterprise is heavily entrenched in Microsoft, of which one factor is that the whole stack is designed around itself (some might call this vendor lock-in). This represents a big, steady revenue stream.
Producing an 'enterprise' client app such as SfB or Teams for the Linux desktop sets a (very small) precedent for validating the Linux desktop as a viable enterprise option. This in turn threatens (albeit lightly) number four above with little to gain in return. No wonder there is little incentive for them to make this a reality at this time. Eventually as the revenue model moves more towards cloud then this will matter less to them, so no doubt far down the track we might see some progress.