See above.

There is are many solutions, including suggestions within the links I posted. There are dozens more about the same topic here. Making excuses for that behaviour says something.

40 people waiting for a lav? Really? How often does this occur? Were they all lined up waiting? Did the FAs permit this?

I think that most rational people do not appreciate a soiled diaper change where other people are sitting, and eating.

I'm quite certain that based on the feedback from crew who have posted here over the years that if they are made aware of the situation they will assist as best as possible to avoid anyone contaminating a seat in that fashion.