Please could you tell me: Why no "pas" in the sentence "qui ne cessent de grimper"?

In this context, pas is optional, and I suppose omitting it is more elegant.

https://www.larousse.fr/dictionnaires/francais/cesser/14343

Ne cesser de / ne pas cesser de. Si ne pas cesser de a le sens de « se poursuivre sans interruption », pas peut être omis : un après-midi où il n'avait cessé de pleuvoir. Si ne pas cesser de signifie « ne pas arrêter de, ne pas interrompre », pas est nécessaire : Pierre n'a toujours pas cessé de fumer, alors que Paul, lui, s'est arrêté.

Bonjour Elaine,

In this context, the mortgage costs situation appears to be constantly increasing.

https://www.wordreference.com/fren/cesser

"ne cesser de faire (qch)"

Hope this helps.

Bonne journée

Jim

Elaine, 

this is ‘ ne littéraire ‘ a negation that omits the following ‘ pas ‘. It is not to be confused with ‘ ne explétif ‘ which is not a negation. Both are mostly used in formal writing.

‘ Ne littéraire ‘ is not restricted to use with cesser - there are several verbs, and a number of situations, that allow use of this structure of negation without following the verb with ‘ pas ‘.

See links to Laura Lawless for more detail. I can’t find a lesson it on it here, or a ‘language example‘ note.

https://www.lawlessfrench.com/grammar/ne-litteraire/

 https://www.lawlessfrench.com/grammar/ne-expletif/ 

NB Laura’s comment on cesser being 1 of 3 verbs that never needs ‘ pas ‘ is not the same as the description given in Larousse. 

As far as I know, using the ne littéraire is never ‘ obligatory ‘, so apart from being aware of it for recognition, there seems to me little purpose in investing much time understanding or learning its nuances,  except maybe for a high formal level of French writing.