IEEE and ACM gives very different results

Me and my colleague are conducting a literature search that will be used to argue about an experiment. We've just started our SLR and noticed that ACM and IEEE gives very different results.

When searching for "java AND jax+rs", ACM gives 26 hits while IEEE gives 18577 hits when searching for "java AND jax+rs". The term "java AND jersey" gives 25 hits at ACM and 701 hits at IEEE. In other searches, such as "auth AND oauth*", ACM gives 62 hits while IEEE gives 65 hits.

We are using the same filters in both searches (limit to journals and proceedings, all years, metadata only). When searching at ACM we limit the publisher to ACM only, and at IEEE we limit publisher to IEEE.

Are these types of results usual? I understand that they are different publishers and thus publishes different papers but these results seem off.