because from my experience if you are traveling to several countries, let's say you are coming from the Philippines or Laos, you will not be able to withdraw us dollars from ATM. Moreover, you will have to withdraw from the ATM many times as the machine will not allow
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baht equivalent in one withdrawal, that will charge more commission. Then when arriving to Thailand you will be stuck with this foreign currency. In case of money Laos that's even a bigger pain in the ass as no change will agree to exchange them to baht.
Believe me that's very annoying (speaking from experience). Hope now you understand. Not everyone comes directly from their home country. But yeah rules are rules and it is what it is.
Which extension did you tried to obtain? You can't get 30 days extension. However, if you vring your wife with you, you can get the 60 days visiting Thai family extension once per visa.
That's the same all over the world. Doesn't make these senseless laws right though. A person has zero say where he was born, where he wants to live and work. No one can choose. All that those immigration officers around the world tells you is "go home!" What if I don't have home and doesn't feel belong.