I find it pretty unlikely that piece of windows software doesn't have a Linux alternative.

Well if you have a very specific software than it may not have an alternative.

People are also ignorant of what Linux is or what an OS is in general. My brother is not tech savy but he's not computer illiterate either. He told me that he didn't want to have to learn how to code to use Linux. I told him that he didn't have to and that he'd be perfectly confortable with it and he didn't believe me. They just don't want to bother. Someone, I believe it may have been Linus Torvalds, said that the only reason that Linux/Android was dominating the mobile market was because it came shipped with the devices. Even if alternatives were available, no one would bother changing.

And even if it doesn't, is it really that hard to setup a dual boot?

From what I can see with my parents and my family, it's not that they find it hard. It's that they are not very resourceful. My parents will call for my help if they get an error message even if the error message is incredibly clear. I had to tell my mother a billion times to restart the computer first before asking me for help. If I have a problem I can word it in a way that will give me the best results. But having the answer is only half the solution. You have to understand it. If I told my mother to google how to dual boot even if the instructions where super simple she wouldn't understand it.