Why is there a 2000 baht fee to exit Thailand at Wang Prachan border post and return the same day?

There is no fee to exit Thailand. And there is no “service fee” to make a smooth run. What does occasionally exist is outright corruption, extortion, and misuse of power by little despots in uniforms. One of the more ugly sides of Thailand (and even worse so in some neighboring countries). It is not like that (immigration) officers “can do whatever they want”. Unfortunately the means to stand your ground and to refuse and appeal are limited, lengthy and complicated. It seems that Thailand doesn’t really take the fight against corruption even remotely serious enough, or they would enable people to report and defend themselves against such unlawful actions. Nothing in the law (immigration act) states that one has to stay in a third country at least one night before returning - made up on the go as other things, too. But it is what it is for now. So, if you want to avoid friction, just extend a border bounce to a short trip abroad, enjoy a night or two abroad with those 2,000 THB instead.

Because they know you are playing the system yourself, so they play the system too

Because people pay it

It cost a lot of baht to run a coffee machine and snack bar out there at the border. won't deliver out there

Because they have found that people won’t pay 3000 baht?

Is this the same for a Laos crossing team ?? That is stay at least one night ??

You might be entering on a VOA...Visa on arrival. This visa is usually valid for 15 days, and costs 2000B

Was it an exit fee or a Visa fee to enter Malaysia?

There's no fee it's what they ask for to make it "Run smoothly" or you have to stay over at least a night in other country

Because all entries are at the discretion of the immigration officer, which means they can do whatever they want in regards to your re-entering Thailand.

There are many borders, especially with Malaysia, that will not let you return at all the same day. You must stay at least 1 night in Malaysia before returning.

someone needs to bring food back home after a long day at work.... ;)