Why is the internal observer called?

Question

Angular

There is such a stream of clicks:

this.createReestrClick
            .pipe(
                switchMap(() => this.documentsRepository.selectedDocumentsFilesIds$),
                tap((ids) => console.log(ids)),
            )
            .subscribe();

In its turn

this.documentsRepository.selectedDocumentsFilesIds$

also broadcasts a stream.

Why even despite the fact that the button is not clicked is an internal stream

switchMap(() => this.documentsRepository.selectedDocumentsFilesIds$),

emitt values?

How to achieve that the stream works only on click - as it is now:

public createReestr() {
        this.createReestrClick.next();
    }

Answer 1

Worked thanks to take(1):

this.createReestrClick
            .pipe(mergeMap(() => this.documentsRepository.selectedDocumentsFilesIds$.pipe(take(1))))
            .subscribe((r) => {
                console.log(r);
            });

Although I don't fully understand why it works like that.