Because the Non Imm O visa only gives you 90 days, they don't know you're applying for an extention of stay and if you do apply its a different Government Department, ie extentions are from RTP and visas from Embassy/Consulate are MFA.
The financial requirements for the 1 year extention of stay are 40,000bt per month or 400,000bt, there's no financial requirement for the 60 days extention of stay.
You certainly can get the 90 days Non Imm O outside the Country, it's available at the RTE Washington DC and just about every Thai Embassy/Consulate. You CANT get the 1 year extention of stay without first having a Non Immigrant O or OA. Most people go for the O as it doesnt require insurance for the extention. STOP confusing yourself and other members!