I think it all boils down to selective enforcement - and the ones who do the selecting are more likely to select whatever puts the most money in certain pockets. How many dozens of times over the years have we seen news articles about the police rounding up the Pattaya City beach nighttime prostitutes, taking them to the police station, fining them 500 baht, and immediately afterwards there they are, right back to plying their trade at the same locations where they were when they were arrested?
How many times have we seen articles where prostitutes were caught stealing from tourists and arrested, but never any articles about whether they faced any consequences at all? I have yet to see an article stating that any of them ended up in prison.
In my opinion if the prostitutes demanding legalization are truly speaking for the majority of those in the field, then they should get it.
There is, of course, a significant difference between legalizing prostitution and decriminalizing prostitution, which would mean while prostitution is still technically illegal, it's not illegal enough to arrest them for it.
I also agree with Dodger's position that it may be best to just let everything remain status quo.