The real costs are externalized.
I find it pretty ridiculous how the carbon taxing is extremely heavy on cars, but pretty much non-existing for air travel here. Tourism is a terrible industry that doesn't even contribute that much to our economy, depletes the housing stock, and removes local businesses and culture, but the tourists are always prioritized by government.
Portugal is heavily dependent on tourism: it's 10% of the GDP. In the EU not even France is that high: Spain is higher but Portugal's economy definitely depends on tourism.
When stats says: "10% is tourism, 40% is services", if you remove the 10% linked to tourism, the services economy does crash too. And so does the 20% that is "construction": a part of that is second effects from tourism.
You can't just say: "We'll just remove 10% of our GDP and we'll be fine". Firstly even at "only" 10% you'd be totally screwed and then anyway the actual number would be much higher.
Where did I say that? I know we're heavily dependent on tourism. I believe a big part of the reason is that tourism has been prioritized over more complex industries for a long time. It's a crutch that doesn't let us evolve our economy.