I don't think, that they really "should". A good practice is to have just SQL Server installed and nothing more, so i could not see any reason to install 18.04 LTS, and not 16.04 which is oficially supported one. BTW, i expect there is a lot of work to rebuild SQL for Linux, which is based on .NET stack. And as far, as i could see - i found only small bugs in JSON parsing ( with JSON_VALUE like functions). And doesn't found problems with performance and/or stability especially with memory usage. I think this is great job, and it's more important, rather then support all version of lib's that could be really diffirent from distro to distro.