answer:I don’t know, but I have some educated guesses: 1) Multiple ways in, due to multiple things with pipe-holes, which may be how they get in there. For example, I have seen crawly things emerge from sink and bathtub/shower drains. 2) Access to water. 3) Access to smelly things that may be edible. 4) Crawly things may also get into sinks and bathtubs and then get stuck there, due to steep slippery sides. 5) Spiders in particular may be there for the other bugs that like the bathroom, since they trap and eat bugs.