Going through your SO phone

Lindsay • Married to a wonderful man! We got married April 4, 2015. We are now TTC #1 and we are super excited and very hopeful!
Just out of curiosity, why do so many people on this app go through their SO's phone? I 100% trust my husband, I have no need to go through it. I am not hiding anything and I'd be upset if he went through my phone without asking.