What they have in common is that they do not interoperate except for XMPP systems which are popular with soldiers and cops. If they did we might have head-to-head competition between clients but instead we have competition between communication networks, and...

There is a certain amount of fragmentation in that they target different markets; I have been on winning teams with Discord but I wouldn't tell people at work to switch from Slack to Discord. Slack Huddles work pretty well but many people use Slack all day and never join a huddle, instead they just use Zoom. Your organization might have an all-access pass to Teams but central IT tells you they'd rather you didn't use it, etc.

Because there are these niches and the because mature platforms decay, there will always be ferment in comms apps.

(2) I think innovation in OS is almost impossible now. One could imagine an OS that eliminates a lot of "bloat" by changing the relationship between the OS and applications, but then you would have to build an entirely new userspace, but if you look like POSIX you can get the GNU tools and so much more.

(3) I would also point to the Innovator's Dilemma by Clayton Christensen

https://en.wikipedia.org/wiki/The_Innovator%27s_Dilemma

as something that execs had heard of by 2007, so when it looked like laptops could be disrupted by tablets, Microsoft disrupted itself with Windows 8. Zuckerberg saw what happened to MySpace and vowed it wasn't going to happen to him. Nobody wants to be the next Kodak...

(4) And film photography is an example of a dethroned platform where a few regional monopolies (Kodak, Fuji, AGFA, ...) made a product that worked with cameras and lenses and stuff. You might still see Bluetooth speakers with the Polaroid brand at Big Lots but many old photo giants are gone. Photography at large is doing better than ever, and some of the old companies like Canon and Nikon went digital. The thing is, Kodak had a working digital camera as early as anyone and introduced all sort of innovation such as the digital Photo CD

https://en.wikipedia.org/wiki/Photo_CD

but it didn't do them any good.