The bigger issue here is that while currently there are quite many communication tools with various degrees of central control, effective encryption, cross platform availability, user adoption, etc., none of them nail a optimum on all these dimensions. You are always compromising on something.

Uneducated users just use what everybody else uses that is "free". This tends to be stuff that is provided by big US based companies like Google, Facebook, Apple, etc. Free here is primarily about pricing and convenience. Recently, people value encryption a bit more but most users lack the expertise to make good decisions for this. So, they'll use something that supports encryption without realizing that might need configuration or turning on.

Companies have to deal with employees using non-sanctioned devices and solutions (i.e. uneducated users), which means the above tools are used. Additionally, they tend to have internal tools that are required to used for internal communication. Typically these too are provided by big US based companies (Slack, Microsoft, Facebook, Google) but are optimized for corporate requirements (better security, team features). A problem with these tools is that they are useless for communicating with people outside the company. Most companies are part of a complex supply chain involving companies that typically don't align on this. So, things like Skype, Google Meets, Zoom, etc. are popular in this space. Or email. A surprising amount of communication still happens via unencrypted email.

Finally, educated users tend to pick solutions that are a bit more on the paranoid side of the spectrum when it comes to privacy, encryption, data ownership, etc. Additionally, open source clients and servers are important in this space. Signal, Matrix, etc. are some better known solutions in this space. Unfortunately, these solutions tend to be not widely adopted and make it harder to communicate with "normal" people in the above two groups. I have signal on my phone but less than 99% of my phone book actually is reachable via it (not counting sms messages here for obvious reasons).

Companies are increasingly valuing this type of solutions from a security point of view. Industrial espionage is a thing and it's a thing companies with representatives in countries like China, Russia, or even the US have to worry about. These countries have very active intelligence agencies and a long track record of actively serving local businesses with basically any information they can get their hands on. Therefore companies that care about keeping secrets ought to be highly paranoid about popular solutions controlled by US incs that must be assumed to be actively under the attention of intelligence agencies.

IMHO OSS, federated solutions, with multiple implementations, clients, and no central control is what is needed. Unfortunately the dominant business models in this space favour closed source, non federated solutions with maybe some OSS clients but typically no independent server side implementations. Signal and matrix are exceptions in this space and neither has meaningful (> 1%) traction in the any market. I guess matrix is growing nicely regardless. Also signal has one big flaw: it uses phone numbers for authorizing users. This gives a large amount of control to operators.