I guess the answer to your question is, because the way those routes are secured is by "Thai" standards.
There are some bolts at most Krabi climbing areas, but you will always find "individual" safety added by someone in those routes.
I used everything I could see, because if there are 15 meters from one bolt to the next one, it can´t be a bad idea using those strings instead of not using them :-)
If you watch closely (hanging down next to my upper right leg) you can see the most important item when climbing there: a small towel against the sweat that´s running down a European´s face and body when climbing in warm and wet areas like Thailand.
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