Skype, when WLM was shut down, was _very_ primitive in its communication options, let alone moderation tools. Sure, things like TeamSpeak and whatnot existed for organized voice chat, but that's not something my mother would be able to use. Skype didn't even have group voice calls back then, let alone video. Emoticons are still limited to the standard ones (or nowadays, seasonal sponsored emoticons), group chat moderation is limited to text commands with no accompanying visual interface (it is not even possible to show who is a group's moderator or owner). Heck, Discord and alike still don't even allow multi-window messaging!

Not to mention the client itself never lasted more than a couple years without a full interface redesign.

Of course, in an ideal world I'd love for some sort of standard interface that allowed me to locally confederate all my services, but sadly Slack and Discord both have TOS rules that require the use of _their_ client, even though their bot APIs are basically feature-complete.

There are quite a few examples of this, both industry wide and specifically from MS. Sometimes it is due to the first implementation being bad, sometimes it is that some part of the tech simply isn't quite ready (or isn't yet quite cheap enough for mass adoption), sometimes it is solving a problem that at the time is very niche but later becomes a more common need.

Think tablets. Anyone else remember MS's big "pen computing" push with tablet & hybrid style PCs that were too heavy, ran too warm, and didn't have batteries that lasted long enough? Or in a similar vain, more general and arguably more successful in their time, PDAs which died out but our phones basically now fill the same role.

There is no shipping messaging client that is a material improvement over what was available in 2000.

https://developer.pidgin.im/wiki/ThirdPartyPlugins

Can I use them on Android?

Although it's probably the best voip and video conferencing software they have put out.