Got any source to back up this claim? Plenty of regions with strong tourism industries have other viable industries. San Francisco, LA, and New York are all heavy tourist destinations but no reasonable person would say that this tourism has made unrelated economic activity less viable. Same with London and Paris. Large tourism industry, but plenty of other industries.

It may be true that as other economic opportunities are exhausted, communities try to use tourism to bring in money to the community (e.g. Leavenwoth, WA https://en.wikipedia.org/wiki/Leavenworth,_Washington). Underdeveloped countries that don't have the ability to participate in many industries lean on tourism more heavily (especially eco-tourism since the lack of development is actually an asset for that industry) which makes tourism take up a larger proportion of their GDP.

But I am highly skeptical of your claim of a causal link between growth of tourism and inability to sustain other industries.