Modern chat apps work better and have more functionality. The knowhow is specifically for Windows chat apps. And the reason the knowledge was lost is that Microsoft sucked at platform design so people stopped learning their platforms and the people who still have the knowledge don't want to go down the career dead end of writing apps for them.

This is partly because MS became insanely complacent. The Windows team is very junior. Just ask anyone who has worked with them. They don't have the skills or resourcing that they did in the 90s.