It feels ridiculous to see a 5-page paper with a 150-page appendix. Makes you question what is the paper.
As it should be. There’s no point doing research if you don’t publish all the relevant information. Now that journals are electronic, you can and there’s no excuse not to.
If you don’t know why the appendix exists, try reading it.
No need to rush to conclusions, I do read appendices when needed. My point is not that authors should cut the appendices or compromise on any other good open science practices. The point is that disproportionately large appendices make one wonder if some of that stuff actually belongs in the main text. If it is just a robustness check that gives a similar result, fine, make a footnote in the main text and put the analysis in the appendix. But what if it is actually relevant information that changes the perception of the main text?