Why shops etc. are over staffed in Thailand?

I've noticed that there are a lot of employees in various shops, often half of employees would probably complete the job needed, so why companies hire that many? Most places are overstaffed from business perspective. Obviously they have to pay them salary so it decreases their profits. As a customer of course I'm happy about it and happy that many people have jobs but am just curious to know logic behind it.

For example at the airport there was a guy who just kept doing hand movement of showing people to keep walking, well obviously everyone would keep walking even without him showing that, there were barriers so only one way to go.