This answer is written with a background of a subfield of applied CS, where conferences are a primary venue of publications.
tl;dr: Yes, it is normal. At the same time, it is unusual (though not "seen as weird") for someone to actually attend all conferences related to their field.
Indeed, it can be a good idea to attend a conference simply out of interest for the topic. Both learning about new research and especially making connections with other researchers are worthwhile goals.
However, there are a number of reasons why it might not be realistically feasible:
- Some employers would not want to regularly cover travel expenses to conferences unless the attendee is presenting something ("has to go") there, especially if they take place far away. To clarify, presenting something on the conference counts as a compelling reason that requires attendance (even if it means the person gets to attend 5 or more conferences in a single year), while simply attending out of mere interest does not.
- As suggested by JiK, there are also arrangements where the total number of conferences that will be funded within a given timespan is restricted by an upper limit. In such cases, "saving" conference trips for the instances where you actually can present something may be the way to go.
- Even if the conference takes place very closely, registration fees are sometimes considerable (600€ or more).
- The time required to travel or at least to attend the conference is missing elsewhere. It is "just" a few days, but it is a few days ever so often that the conference attendee will not be available for progressing with their research and fulfilling their possible other duties (e.g. giving or supporting classes, supervising students, performing non-research tasks required by their funding source and/or department, etc.). This is especially difficult with regular (e.g. teaching-related) duties, as they cannot just be postponed; someone has to fill in for the traveling researcher.
Moreover, the value of visiting these conferences (especially compared to other strategies for using your time that restrict conference visits to when you also present something yourself) should not be overestimated:
- While a conference can usually be picked for being "on-topic" for your research, most conference scopes are often still wide enough so the vast majority of works presented there are at best "nice to see, though essentially unrelated" to your work (especially in early stages of your PhD, where you are probably somewhat focused on rather narrow topics, as opposed to more senior researchers, who are more likely to be interested in a whole bunch of topics covered by their own group).
- This is less of a concern for workshops, which are usually more focused on a specific topic or set of questions. On the other hand, workshops (at least as I know them from some CS-subdisciplines) often have lesser requirements to the completeness of contributions, and also sometimes later deadlines than the main conference. As such, it can be easier to still produce something to present on a workshop as a "justification" to attend the workshop (and also the conference it is embedded in).
- While some talks are certainly interesting to watch, not all of them are. A bit of personal preference towards receiving information in talks vs. in writing certainly plays into this. Still, I think it can generally be said that attending a conference is not an overly efficient means to quickly get updated on a wide spectrum of new ideas, given that every single such idea occupies a timeslot of some 20 to 25 minutes.
- Finding new contacts tends to be a bit of a "gamble" that is, among other factors, influenced by the nature of the conference. Especially smaller conferences can easily have something like a "core community" that considers the conference their "annual meeting of old friends", where it is very difficult to get into. Again, this depends a lot on your personality, of course; different people are very differently skilled at getting in touch with strangers.