[JohnTHaller]

It's still relatively early (they're on rapid release, so 15, 16, 17, 18 don't mean what they used to) and Linux is a tiny sliver of a market for the Opera folks. Opera seems more focused on achieving commercial success across modern mobile devices (as opposed to the dying feature phone business) as well as desktop browsers. Dropping the old rendering engine helps them towards that goal (for good or ill). Delivering on a Linux build at this point probably doesn't.

They have a lot of development time to still put into the new Opera builds full stop. And making them work on the most popular platforms (with the most users and thus the most revenue from partnering) makes sense. Mac is about 1/12th the userbase of Windows. Linux is about 1/5th the market share of Mac. So, it would be the last in line to get work put into it.