> Because we have too many other tools we also need.

Yes, but secure messaging is a well understood domain I suppose so it's the kind of app that is simple(not easy) to write and most tools compete on UX. A lot of tools on the list at the end have complex domains that are not that well understood by stock developers, or they might require a lot of R&D or actually talking to teams that have a problem to solve.

Furthermore it is extremely difficult to market a lot of these tools to corporations. IM? it's fairly easy.

The situation with secure messaging apps today isn't so different than social networks in the 2000's. It's a formula and it's easier to raise capital on that formula at the moment.