a country that mostly relies on tourism is set for being a unstable and poor.
Tourism relies on only a few scenic or historically interesting locations within a country. It doesn't require an entire country's population to support this.
Even if other jobs like in hotels and restaurants are created, tourism can be seasonal and people don't often return to the same places when they holiday because they are always looking for something new. That or they had a very bad experience especially from other loutish tourist (like all the British who go abroad on once in a lifetime dirt cheap package holidays because they will never afford one again).
The tourism industry doesn't require any great skills and so the wages are usually very low. Some countries rely on foreign migrants to support their tourism industries because of this. But this can put tourists off especially when they are paying for an experience and looking for local authenticity but it isn't there. Indeed, who wants to visit places like Poznan, Wroclaw, Gdansk, Warsaw, etc. and run into native English speakers from the UK? E
This is why Poland has a very diverse economy that supports Polish jobs in Poland for native Polish workers.