You don't have to wonder, because they are. They're manifestations of fields.
I think it is a reasonable answer to tell people "if you're looking for the short list of simplest things, the number of types of fields there are is probably what you're looking for".
That doesn't invalidate this question in general, though the number of different answers from people looking at the same thing suggests it may be underspecified.
That's what the various string theory proponents start from. There's "too many" different subatomic particles, so there surely must be something smaller that they're composed of?
As usual, the hard problem is how you define "Elementary" which is why the posters always show 17, and then you get numbers that go as high as 995.5 (and the .5 is an interesting result as well).
Might there have been a point in time (long ago) where the “wave photon” and the “particle photon” seemed like possibly different things?