Technology doesn't have to be the answer for everything.
There is potentially a lot of information I want to share, and it would be weird to have dozens of notes all over the house. Plus it would be fairly natural for the renters to read them and then immediately remove them, and then, weeks later, forget what they said; "Wait, what's the trick to getting the bath temperature right? Wish I hadn't removed that sticky note!"
Also, I can spend the next week+ building up the "library" of notes as I go through the house, vs. having to do it as a "last chore" before we leave the house, putting sticky notes all over the darn place and trying to prevent my 3 and 5 year old children from grabbing them.
And we could re-use the virtual notes with zero effort the next time we rent the house.