It doesn stink; insurance companies operate on long experience and statistics.
Which they won't show - which I suspect is because they often don't fully support the penalty imposed on people with diagnosed/treated pre-existing health conditions.
They know that people with a pre-existing health condition are more likely to fall ill, especially under the stress of travel. They are not punishing you, they are running a business, which employs people and has to make profits so they have a responsibility to get these things right.
They know it, do they? I'd bet they can't support that belief fully with data because of things like:
1. Some don't actually ask about all pre-existing health conditions. They just ask about those being treated, usually within the last two years. So if I refused treatment, after two years, those insurers would cover me much more cheaply, despite me being a much higher risk.

2. Very few actually ask about the effect of treatment and whether test results are satisfactory or what those results are. I'm told even my most serious condition basically poses no risk if treated to satisfaction (I'm no more likely to fall ill than someone without it - possibly even slightly less because 1 in 500 have it and most are undiagnosed until they fall ill), yet most insurers don't even ask about the treatment effect. I could be taking sugar pills and vinegar and some insurers wouldn't be able to tell from the questions they ask

3. If I'd declined all diagnostic tests despite genetic indications that I'd have the condition, they'd insure me including my illnesses (which I would still have but wouldn't know about) with no penalty.

4. And I think this is the clincher: the range of penalty loadings imposed for my condition in one year's quotes for similar cover range from about 25% to over 1000%. That's probably not based on likelihoods - that smells like some insurers using pricing to say "fark off, crip".
They should have a responsibility to get these things right, but they don't.
And "the stress of travel"? It's a farking holiday. It ain't stressful, especially not compared to some jobs (I have other insurance for work trips - which bizarrely never asks about health). If they believed that, insurers would add some questions to the quotation process to try to figure out if someone gets stressed by travel.
Can you imagine how long they would survive as businesses if they took a chummy relaxed attitude to risky clients and ended up paying out for all kinds of claims? Big insurance companies employ or support thousands so a failure would cause misery to many.
They are taking a chummy relaxed attitude to risky clients - the clients who don't even take diagnostic tests get the best prices. Surely they're higher risk than people with benign treated chronic conditions?
Some big insurance companies are discriminating against thousands, so are already causing misery to many!