Only makes sense if there is no money left.
I'm pretty sure they tried very hard indeed. They just didn't succeed.
I say this as a long-time user of Ubuntu Touch. I don't love it, it is not without its flaws. It's just the best mobile OS I've found, primarily because it doesn't nag you with privacy-invasion at every turn. I'll miss it when it's gone.
I don't know about this. The last phone they released was the Meizu Pro 5, which had an Android variant (sold in stores) and an Ubuntu variant (sold online only, and you had to dig for it if you didn't get redirected from ubuntu.com). The hardware itself for the phone wasn't awful by any means, but buying one was hard enough because the manufacturer only sold out of Asia.
Further, the Meizu Pro 5 didn't work on most networks in Canada and the United States. Why would I buy a phone that doesn't support 3G/4G? I'd _love_ to support Canonical by purchasing an Ubuntu touch device, but you could hardly say that they tried. Their handsets were few and far between, and they locked out a large portion of the market because of the phone's baseband frequencies.
I think that they could have succeeded, at least in the small, had they actually released a device that power users could use comfortably.
Having said that, I am not sure why? Ubuntu Phone seems largely functional on a few devices, but installing it and using it remains a pain.