It's a more 90's aesthetic where materials were available but not the finances to hire someone to do it well, so people did stuff like wallpaper by themselves instead with varying degrees of success.
People still do that, though maybe less. Men in the family are electricians, masons, plumbers, all at the same time, and with varying degrees of success.
Yes, but you can now afford better tools and materials, online tutorials and tool rentals exist, which can improve your odds a lot with a little preparation.
Edit: I live in an apartment where a construction worker used to live. It's full of dumb kludges and half jobs, or as slavs would call it, "khaltura".
No matter how good your tools and materials, a skilled enough amateur can fuck it up. You can't account for taste either. Furniture shapes aside, those bed covers and the couch are also not something I'd have in my house.