Observable subscribe vs pipe - rxjs - rxjs

Question

I have following function in service to retrieve data:
public getData(): Observable<dataObj> {
const endpointURL = 'xyz';
return response = this.responseHandler
.makeRequest<dataObj>('get', endpointURL)
.pipe(
startWithTap(() => this._requestsInProgress.next(++this.requestsInProgress)),
finalize(() => this._requestsInProgress.next(--this.requestsInProgress))
)
}
in different place I have something like this and I call that function:
export class SearchAndFilterService {
private _data: BehaviorSubject<dataObj> = new BehaviorSubject(null);
private _searchTerm: BehaviorSubject<string> = new BehaviorSubject(null);
private _filterTerms: BehaviorSubject<string[]> = new BehaviorSubject(null);
public readonly data$: Observable<dataObj>;
constructor(
private service: Service
) {
this.data$ = combineLatest([
this._data.asObservable(),
this._searchTerm.asObservable(),
this._filterTerms.asObservable()
]).pipe(
map((tuple) => {
const [data, searchTerm, filterTerms] = tuple;
if (data) {
return {
...data,
array: this.searchAndFilterData(
data?.array,
searchTerm,
filterTerms
)
};
}
return data;
}),
);
}
public updateDonorAppointments() {
this.service.getData().pipe(tap(
(data) => this._data.next(data)
))
}
I thought that pipe should create a subscription to returned observable and this will work. However instead of pipe I must use .subscribe to make it work. Like this:
public updateDonorAppointments() {
this.service.getData().subscribe(
(data) => this._data.next(data)
)
}
Am I missing something? Or is this approach totally wrong?
Thanks