This is the reason Mozilla became actually very, very consumer oriented. It really doesn't care about business users - but of course you don't pay for its software so you can hardly blame them.
Within Mozilla business model, it's hard to make money from a mail client - and thereby no reason to invest in its development.
LibreOffice could try to add it to its office suite in an attempt to counteract Outlook somehow in the business space - today is especially the business user needing a fat mail client - yet if enough resources are available is to be discovered...
Biting the hand that feeds IT
