I am not sure if this is the real reason. C++ is still a very valid option. People used to low level languages can rather easy switch the language they are writing in.

Maybe one day we will find out the real reason.

Of course this is a matter of how well the maintainers took care of tech debt. Additionally, architectural changes are often not possible or only if you put a lot of effort in it.

You are certainly right at this point. To be honest, I have never looked at the source of LibreOffice and it might be a huge mess. Additionally, the maintainers need to be somewhat cooperative. I could imagine that this is also a problem (developing many years of FOSS makes your personality really toxic unfortunately)

So old code is now suddenly bad? Weird and somewhat also not the case, as LibreOffice is constantly updated.

I guess it is a preference. I for myself tend to rather use a FreeBSD than Fedora for production environments.

Why don’t they contribute to LibreOffice Online?