I think that companies that are on Linux don't necessarily want to pay the SQL Server license costs. Windows server licenses are cheap compared to those of SQL Server. (Unless there's that many people that like SQL Server and detest Windows server. I know Windows 10 "features" have managed to irritate plenty of experienced users.)
If you want to stick to a database or two, you can also stick to a operating system or two. If your staff knows Linux, MySQL, Postgres and SQLite, adding in SQL Server means there's an expensive learning curve. 😛
I like my mostly separate Linux and Windows worlds and can manage them without mixing them together like chocolate cake and Brussel sprouts. I know companies that can handle both. But some of the hybrids purposed by Redmond don't make sense in the OSS world.
There are plenty of companies that pay the SQL Server cost and the Windows cost, and aren't happy because those are the only Windows boxes in the DC. It's not a hug number in absolutes, but it's large enough that MS made the effort to move here. Those companies want to stick to only *Nix inside their org.
It's not that they can't handle it. They do, but don't like it.
I guess if they have dedicated applications that only run on SQL Server. Most companies I know aren't that Linux-bound, they usually have some sort of small group of folks that need Windows and it's applications in addition to SQL Server. (There isn't true Excel equivalent in the OSS world.)
Or just spinning SQL Server on Linux in ""Cloud"" is easier than on Windows.
Still somewhere, there has to be a Windows VM or native imagine to manage the SQL Server. SOS and the other ported tools aren't ready for prime time yet.
Or since all the TOP 500 Super Computers are Linux based, maybe SQL Server is a target for one of them... 😛