Or because they are not new. I had a bad experience after i bought, in January 2016, Intel NUC with Skylake processor and Iris 530 graphics card.
I had few months of struggle, like:
- problem with installation (installer won't boot without some cryptic kernel parameters passed),
- lack of graphics driver
- random crashes (like Google Maps causing the whole system to hang, requiring hard reset)
- processor not running at full speed
- system seeing only one logical core instead of 4 (2 cores x HT)
- "shutdown" system button causing reboot instead of power off
Most of those were fixed only after Ubuntu 16.04 came out, at the end of April. Some issues however, persist.
So, my impression is that Linux is good choice only if your hardware is quite old (like, say, two years, or at least one processor / graphic card generation behind)
For people like me, who want latest and greatest hardware Linux is not an option.
On the other hand my mother's friend had a mysterious driver problem (screen glitching) with his NVidia card after upgrading to Windows 10.