Why every day?

it's a part of my routine. my day isn't complete otherwise

I try to move every day - most of that is through my routine, structured programs or it could be as simple as an easy walk/jog on the weekend. But there are some days that my body needs the rest. I can tell - it's a totally different type of tired than my usual "ugh, it's 4:30am" tired. On those days, I take the rest...and I don't beat myself up over it.

I wouldn't say I get stressed if I missed a day, but fitness is very important to me and I look forward to my workouts.

I work a very sedentary IT job and I don't get in much activity outside of exercise.

Exercise makes me feel amazing, it keeps me fit and healthy and I really love the results it gives my body. I love my walks, weights and Pilates!

I'm maintaining so I don't workout for the calorie burn. It just a habit for me now and I like to move it, move it.

I run 40-60 minutes 6 days a week. I do plan a rest day because it's also nice to rest and do something else. I had two stress fractures because I would do this everyday and it was apparently too much for my bones - but that was before I learnt the lesson. That's only my humble personal experience

Or maybe it's partly things like this, from the US Centers for Disease Control:

https://www.cdc.gov/physicalactivity/basics/adults/index.htm

that recommend 150 minutes of moderate-intensity aerobic activity per week, plus at least 2 days of muscle-strengthening activities per week . . . which one sees translated in other places to "30 minutes a day of aerobic activity 5 days per week, plus 2 days strength training" (or some such)? Starts to sound like working out every day, one might think.

If the real question is "why be obsessive about it", well, once people think they need a habit, it's pretty easy to be obsessive about it, and stress about missing the target. Also, I'm always amazed at how much people want to catastrophize, and create drama for themselves - on many fronts, not just this one.

Considering the source (i.e., what I know about OP, as one of her MFP friends), I doubt the underlying question ignores the idea that some people have training or fitness goals, or feel better when they work out. I'm thinking the emphasis is more why the stress (freak out) if one misses a rare day (just because of missing), or hesitancy to take a rest day, even when a rest day is clearly needed based on other things the person happens to be saying at the time. At times, rest days are a necessary part of the process.

I lift 4 days a week and have a set schedule/plan for each of those days. When I miss one of those 4 workouts the plan kind of gets messed up, but it doesn't bother me.
The other 3 days are what I consider rest days. I enjoy my rest days.

I train Monday through Friday, rest on Saturday. I'm also involved in action pistol shooting. Which I normally try to do every Sunday during the season. I need my rest.