I am fairly sure the issue isn't medical: I can code, drive, and read for hours at a time without losing focus. But meditation is still torture (as is having to sit down and watch TV). I have tried several times, I have done it every day for up to two or three weeks (willpower is not really an issue) but every time, after a while, I ended up feeling more trepidation and anxiety about doing it.
In addition though, I think there are good reasons to prefer exercise in certain cases (YMMV, and this is just my experience):
Stressing your cardiovascular system mimics the physical effect of a panic attack. And part of the reason that panic attacks occur is because something is wrong with the link between the physical and mental parts of the system. You can't solve it with looking at one side alone but it is useful to experience the physical sensation of panic without the mental side (hopefully, it can set things off). I don't meditation is as effective on the physical side, it may be effective on the mental side but not for me.
This is not going to be relevant for 95% of people. But it has been my experience of it. I also think it is pretty unwise to say it should work for everyone. If you get the impression that should work for everyone, and then you try and it doesn't work...you feel terrible (if you have a disorder, it is worse...you might feel shame). Unf, in my experience, this is fairly common within psychology too which has endless "universal"-sounding solutions with weak effect. It just isn't that simple. Try stuff. See what works.
Again, hopefully this will help someone. The number of times that I have tried meditation should suggest that I was convinced, past the point of logic, that I was the issue...not meditation...unsurprisingly, that belief elicited little progress. It makes more sense to just do what works.