It did not get changed.

Windows Powershell is up until 5.1 because it runs ONLY on Windows.

Powershell 6 was named Powershell Core due to being built with .NET Core. It was not fully compatible with 5.1 and lacked some functions based on the WinApi.

PowerShell 7 is still built on .NET Core, but has a much better compatibility with 5.1. They dropped Core because nobody cared and it's shorter and works equally well on all platforms.

So Powershell is the v7 and Windows Powershell is the old 5.1. Nowhere is that confusing.