Earlier quoted context omitted.
In my area, you get 10 days of unexcused absence per year before parents and kids start receiving fines and possibly a referral to CPS. That number is way too small IMO, and it forces folks to go to the doctor constantly for getting small illnesses excused (school policies are 24 hours without a fever, but they don't take temperatures, it's honor based...), since you want to keep those 10 days for an actual vacation.
Why would you take your kids on a vacation during school? There are plenty of breaks during the year including all of summer.
When everyone else is doing the same thing. If you do it at a different time you could benefit from reduced costs and reduced traffic. You can also provide your child with a more rewarding and engaging experience than the drudgery and frustrating inefficiency of the typical school pedagogy.