The major airports are run by AoT, and the small provincial airports by the Department of Airports. CAAT is a regulatory agency that doesn't operate airports, so why are they the ones pushing this?
It was raised a year ago, but why let facts get in the way of a good story?
https://www.airportthai.co.th/en/aot-will-adjust-its-passenger-service-charge-psc-of-international-and-domestic-passenger/#
First of all, Changi provides far better service than BKK, so that's a foolish comparison. Also, they cherry-picked that example, since the PSC at BKK is higher than those in Seoul, Tokyo, KL, and Taipei, and similar to Hong Kong - and most of those airports are much more passenger-friendly than Suvarnabhumi.
What a remarkable coincidence that this is exactly what Thaksin said in a speech a week ago...
https://www.bangkokpost.com/business/general/3071305/thaksin-touts-golden-visa-higher-travel-fees-to-boost-thailand