Easy to use, sure, but I've only known four GUI systems to be built to high assurance standard: simple components, small TCB, and clear interactions. Mainstream OS's don't use them. People adding beauty to their apps on such OS's also add attack surface in most cases. So, people wanting easy-to-use, secure communications must accept simpler interfaces or maybe text-interfaces depending on their threat profile.

I'll agree the interface needs to be easy to use regardless of how it's implemented. Most tools that aren't got that way due to lack of solid effort into UX. They can certainly do better. Yet, the result might look like a console IRC client or an old Win32 GUI app if it uses simplest stuff for security. Will users embrace that? Unlikely & didn't for many commercial products in this space. It's why the person you replied to is right: they won't make the smallest sacrifices to solve their greatest problems.

Has always been the case. Intel has lost over a billion dollars the few times they tried to market something more reliable and secure. It wasn't backwards compatible with crud X or support risk Y. So, market killed it off to buy stuff that causes problems. Trend repeats in all areas with few exceptions. It's why high security & reliability, even inexpensive offers, stay a niche market.