do it yourself, and you have no guarantees you are bringing in all the documents, standing in the right line, etc. Not everyone has time to waste navigating bureaucracy. Paying agents is out of necessity, not privilege.
Grammatically, English is much harder (and let's not get started with Romance, Germanic, Slavic...Latin!), but for our western ears we aren't accustomed to monosyllables at differing tones, but also... Thais seem to break completely if you get them wrong while expecting us to understand when they mishandle verb tenses.
I still find it amazing that Thailand hasn't yet made illegal for its citizens to enter the country with a foreign nationality passport. That is illegal in
not al immigrants are created equal, but there is little doubt that educated and/or self financing immigrants aren't a net plus for the receiving country.