I believe such organisations tend to do such things very intentionally :-)

About ESO [1]

> We are an intergovernmental organisation established in 1962 supported by 16 Member States (Austria, Belgium, Czechia, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), our host country Chile and strategic partners.

So Chile has a distinct status, hence the margin...?

[1]: https://www.eso.org/public/about-eso/