I think that above all achievable targets are the thing. I always start from "something is better than nothing." Maybe I am just too easily demoralized, but if I start with great ideas, my progress tends to stall after a couple of weeks. If I build up, I can keep it going for longer.
So I would say, three times a week is better than not at all. If it is manageable for you and it gives clear benefits, then why change it?
If it is not working for you, you can always try a different routine - say, shorter walks every day instead. Or a longer walk every day, if you find time and feel the benefit.
The reason I gave the thread this title is because there is masses of research that says we benefit from exactly this. It's great to do wonderful things in sport and fitness, but for our health moderate exercise is both necessary AND sufficient. So, for me, I am just trying to stick to this as a "baseline".
In my case, I do find that three longish walks a week are enough to keep my blood sugar stable and my insulin resistance low. I'm T1 so it's quite easy to measure insulin resistance by insulin requirements. I find that if I slack off for four days, I start to see my blood sugars creeping upward. But it doesn't have to be a great effort to get back to the right place. A bit less sitting down, a bit more housework, half an hour's walking can do it.
I like to do more because it starts to push my insulin requirements down, which is all to the good in my opinion. I don't want to be an insulin-resistant T1. I think that would be more than I could handle.
There must be some variation between individuals, of course. I know the more muscle you carry, the lower your insulin resistance. So more muscular people probably can slack for a bit longer. (When I used to run a bit in my youth, I was always long-distance and cross-country, not a sprinter at all. So I'm pretty puny!)
That was a bit of a ramble so the short answer is no, I don't think you do have to exercise every day!