Why don't many hotels provide toothpaste as part of the toiletries supplies?

What goes into your toiletry kit varies from region to region. No quality hotel in Asia would neglect your toothpaste, or toothbrush. But it is true that Hyatt is the only major North American chain to offer it as a standard.

Daniel Engber of Slate magazine wrote a lengthy report on this very question in 2013 entitled The Mystery of the Missing Hotel Toothpaste. He interviewed executives at 18 different North American hotel chains, and received the same excuses:

1. Their consumer research indicates that guests don't want toothpaste.
2. The industry norm is not to provide toothpaste; their competitors don't offer it, and independent hotel ratings firms don't grade it. For example, the AAA Diamond Ratings Guide criteria require escalating amounts of soaps, lotions, and so on, but not toothpaste.

Independently, there are other theories. One is that toothpaste, because it is considered a drug, is more expensive to manufacture, and gets excluded for cost. Another theory is that the toiletries are there for marketing, not practical purposes— there are luxury soaps and lotions to flatter the guest, but there is no such thing as aspirational toothpaste. Another is that people are likely to bring their own, since it is less likely than shampoo or lotion to leak. Yet another is that toothpaste is a more personal item, and so people are less likely to use it (as with hotel-provided deodorant or tampons). But these are all just speculation. He concludes

We don’t get toothpaste in our rooms because we don’t ask for toothpaste in our rooms; we don’t ask for toothpaste in our rooms because we never knew we could.

That said, many business and resort hotels do have toothpaste available upon request.