Hi @Soraya205
There are only two reasons that I can think of, maybe some other hosts can think of more.
1) Sometimes hosts don't want to create the expectation so they can exceed it (and hopefully be marked up in the review).
2) If the host isn't always able to offer the items, they may rather not mention it. If it's in the listing, guests can complain if they don't receive it. Perhaps some of the hosts know by now that they sometimes don't have time to re-stock.
The problem with offering something nice only some of the time, is that guests may mention it in their reviews. So even if you don't mention it yourself, a past guest may set the expectation for a future guest! For this reason, I would say it's best to only commit to doing things that you can keep up at every guest changeover.