Why are "pidgins" and "creoles" interesting from the point of view of language change in general?
Pidgins and creoles are interesting from the point of language change because they demonstrate how languages can change when people who speak different languages are brought together and need to communicate.
Pidgins are typically very simple languages with limited vocabularies and without much complexity of syntax. From a linguistic point of view, they are interesting for what they drop that languages typically have. For example, pidgins tend to drop difficult things like tones. They also tend to simplify the pronunciation of words, just as tends to happen in all languages in the long run.
Pidgins (according to some scholars) evolve into creoles like Hawaiian Creole English (which I include because I speak it). As a creole evolves, it often regains some of the features that were lost when the pidgin was developed. It will, for example, regain things like inflectional affixes.
Since pidgins and creoles are languages that (in some cases) are being created and rapidly changing within historical memory, they show us a great deal about how languages change in general.