The entity suggester only returns items, not properties. This is counter-intuitive as Special:Search returns both items and properties by default. For consistency, the entity suggester should include properties too (for instance, searching for P17 should return https://www.wikidata.org/wiki/Property:P17 as first result).
As a user, when looking for a property, I usually go to a random item and pretend I want to add a statement there: this is the only way I can think of to get a property suggester. This does not feel very natural. Using Special:Search can work too of course, but because of the different way the data is indexed there, results can be quite different.