HTC isn't quitting the mobile market entirely, of course, even if it is increasingly difficult to challenge juggernauts like Samsung and Apple. They're just shifting their efforts to focus on mid-range and high-end phones like the upcoming HTC U Ultra shown here. HTC has been bleeding money and they'd like to be profitable again. I think we'd all like to profitable again.
Not only will there be no more cheap HTC smartphones, but the company intends on releasing fewer phones in total in 2017. They're looking at around 6 or 7 devices. The lower-end of the market is just too competitive with too slim a margin, especially if you can't get the kind of volume you desire. Higher end phones have comparatively bigger margins. HTC will continue to support any of the entry-level phones that are already out there. They just won't make any more.