eSIM2Fly is likely not an ‘authorised’ reseller for AIS (same with thaiprepaidcard), so adding their markup over what they are likely paying themselves. Also, they could be pre-registering the cards?
AIS’s target audience is those in Thailand planning on travelling out from there; that S2F works for others is a happy benefit they probably don’t really care about, and may even shut down as KYC becomes more cumbersome (or is being sidestepped altogether).