"I don't understand why Microsoft took so long to do this."
Skype had free video group calls long before Google Hangouts even existed. If I remember correctly, they forced their users to pay for it a few months or a year after Google Hangouts launched, which was a really stupid move which surely helped Google's product a lot.
Group video was only free for a very limited time on the beta only on the Windows application. It became a paid product over a year before Google Hangouts launched.
Skype had free video group calls long before Google Hangouts even existed. If I remember correctly, they forced their users to pay for it a few months or a year after Google Hangouts launched, which was a really stupid move which surely helped Google's product a lot.