answer:Don’t forget the archive feature Gmail gave us – the ability to not delete it AND not see it? Priceless. I think it’s because once email started getting to the Gmail stage, people didn’t need Outlook. Still, many wanted it or something like it, but Thunderbird is free and open source – it can improve much more easily than Outlook. There seems to be a gap between when people didn’t need it, and when they realized they might still wanted it, and Outlook didn’t really improve, and now they have no way to convince people to pay for it when they could get something else free, so they don’t bother.