That suggests it's just a matter of focus. I can open multiple screens on my pc without issue, and switch between windows and tabs easily. I also don't have to worry about auto-correct messing something up, and websites by-and-large have awful mobile sites compared to the default on desktop. The mobile experience is just worse in nearly every way, barring portability.
People who entered the Internet for the first time on a smartphone have already outnumbered those who began surfin' the web on computers. Otherwise opinions like this would be obvious to everyone, as almost any computer screen is massively better and mouse / keyboard control is far more precise.
Eh, it's only been 14 years or so since smartphones reached what I would consider ubiquitous. That definitely leaves a lot of people probably most familiar with smartphones, but I doubt it's the majority. Probably getting close at this point, though.