You don't have a very good imagination.
$8 is nothing. Which is why one day they will double it. $16 is nothing too I guess. Make it $20.
I could totally see some poor hippie backpacking dross being in a predicament about the entry fee when they arrive.
And some ppl will hate the idea of an entry fee on principle.
There are reasons why Thailand hadn't done this 30 years ago.