Many people do not regard writing as "work." This is especially true if you're writing on the side while holding down a full-time job. People see (or imagine) you sitting in a comfortable chair, writing or pecking at a keyboard, and they know that's not work. It can't be: no one is yelling at you, there's no heavy lifting, you're not running around with a look of fear on your face, and you're certainly not building anything anyone can see.
Most of these folks figure you're just goofing off. (Or, as my late, famously alcoholic father, who made a lot of money doing something else entirely, used to put it, "Sitting on your ass all day.")
It gets worse when you are writing full-time. People who see you home all day may assume you aren't working (or you're on the Midnight shift, or selling drugs). Combine being home all day with sitting on your ass, and you're a perfect target for people who figure they can get you to help them garden, move, run errands, or give them a ride somewhere, since you're not really doing anything.
I learned the hard way that you have to say “No” to most such requests. Some people try to get you to agree by whining, begging, threatening—whatever they can think of. But I noticed that every time I took time away from my work for someone, it just encouraged them to impose on me again. And again.
Not long after I started writing for a living, I was forced to adopt a policy of always being on deadline—even if it was invented on the spot.
“I’m really sorry," I would say, "but I have to finish what I’m doing before five o’clock, so I can FedEx it to my editor.” I never discouraged a petitioner from their errands or tasks; I simply excluded myself.
Sometimes, I suggested someone else who might help them, or a different way they could do what they need to do on their own. After a couple of months, people stopped calling for help. A few took it personally, figuring that I didn't drop whatever I was doing to drive them into the city (where the one-way streets confused them) because I didn't care about them. Others thought I was really smart when I came up with a way for them to move that piano without my help.
A very few finally got their heads around the idea that someone could be at home yet still working.
And I got to write.