Not actually "in Excel", though. The Python code runs on Microsoft's servers (they say in the introduction) and Excel is just a client.
There's no reason they couldn't embed CPython in Excel, but maybe the intention was for the online version of Excel to have feature parity without having to compile Python to JavaScript?
the intention is to lock in orgs to their cloud services. This is a value-add. They really know that Excel, Word are "feature complete" and the only way they're going to make money on it is by harvesting and locking in the users.
There's no reason they couldn't embed CPython in Excel, but maybe the intention was for the online version of Excel to have feature parity without having to compile Python to JavaScript?