Because there's no correlation between the ability to organise a village event and the graphic design skills. (Apart from "it's been so successful we can splash money on a design agency") Maybe someone actually liked it and thought it's enough. I've seen groups overthinking posters and it felt similar to groups at uni overthinking funny names instead of doing the work that actually mattered.
To be clear, I'm not saying those designs are good, just that most of the time the design is not the point and minimum effort above "Times New Roman 12pt" is what many people always wanted to do.