Why is the airport tax at some airport charged outside the airfare ticket but instead must be paid at the airport?

Example from Uyuni airport in Bolivia where the airport tax is 11 BOB per passenger:

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  • This is a re-asked question that got closed for lack of attention last time around. – Willeke Feb 15 '20 at 21:19
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    And the answer is likely to boil down to: the government wanted it that way. Acts of governments don't have to make sense, and often don't. – Michael Hampton Feb 16 '20 at 6:14
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    Getting foreign exchange cash directly from travellers, instead of payments from airlines in their own local currency – Ankur Banerjee Feb 21 '20 at 13:32
  • @AnkurBanerjee thanks that sounds like a good reason. Could you please post it as an answer? – Franck Dernoncourt Feb 21 '20 at 17:55
  • I was trying to find a source that could back up my thinking, couldn't find one unfortunately. I do think it's to get forex in cash though, as it helps with the country's reserves. They could of course ask a foreign airline to reimburse them in chosen currency but that's assuming they have IT systems in place handle and reconcile such payments which they might not. It'd be my best guess. – Ankur Banerjee Feb 24 '20 at 16:28