Where?
Reason earlier opening doesnt work very well for BG type beer bars is that sweaty hot farangs are hardly appealing to the ultra odour consious Thai - so as the temperature drops - it makes it more tolerable for the average 'farang' to be comfortable sitting outside in what is a tropical climate.
Year's back bars did open earlier (but there were a lot less bars then) - as some still do, but there is not enough early custom from the shirtless types to make it viable for all to follow.
Girls too have become accustomed to working later, and many dont even wake up until late afternoon - this will not change simply because some moral crusader thinks we should be good boys and girls and go to bed at midnight - I'm certian that given a choice between a laid back vacation without all these daft restrictions many will not waste their hard earned cash to return.