Ardour is great, and so is Reaper. The existence of a solid DAW on Linux isn't the issue at this point.
First, one of the major issues is inertia - Logic Pro, Ableton, ProTools, Cubase, Sonar, and FL Studio are all respected names in the field, with lots of users, forums, and ecosystems around them. Audio engineering is very susceptible to a herd mentality, because anyone who uses something different will be told to join the herd, rather than getting actual support.
Next, audio engineering is much more hardware dependent than most CS/IT disciplines. For us, 'input' basically consists of keyboards and NICs, which are interchangeable. Pro audio involves audio interfaces from Tascam, Presonus, M-Audio, and FocusRite, with MIDI controllers ranging from Korg/Yamaha keyboards to guitar pedals and drum pads. We'll circle back to the interface problems in a moment, but the MIDI controllers are largely USB now, meaning there are abstraction layers that may require specialized drivers, mapping software, and plug-ins.
Back to the audio interface question, amongst the major things we have here is that Jack/Alsa are fine for desktops with Realtek chipsets, but when you're dealing with thousand dollar interfaces that can record sixteen channels of audio in real-time with 1ms latency, Jack and Alsa just don't cut it. OSX has CoreAudio and Windows has ASIO, both of which are industry standards that work with those interfaces. Linux would need something similar to it, but even if such a thing were to come into existence, support by the hardware OEMs is certainly not coming into place overnight. Meanwhile, those OEMs need to sell gear, which means that CoreAudio and ASIO handle over 99% of the market, and no one seems to be chomping at the bit to write yet another audio system for Linux to even provide a viable target. Reaper and Ardour could well start on that, but now you have DAW devs stuck writing middleware that already exists on Windows and OSX.
I look forward to it happening, but it's a pipe dream right now. Hardware OEMs are targeting ASIO and CoreAudio, plug-in writers are targeting Ableton, Protools, and VST hosts, industry standard DAWs are targeting Windows and OSX, and a soup-to-nuts Linux ecosystem would require cooperation from everyone at the same time for a market segment that's super picky at best.