I always remember many verbs ending in -ing.
Swimming club/cap and shaving foam for example. I now see increased use of swim club and shave foam.
Why has this happened, is it correct use of English ?
I don't think that there is any one thing happening here; there is no grammar conspiracy behind this.
Even between similar (swim[ming] team and swim[ming] cap) pairs, there is no pattern. (If you look closely swim team and swimming cap have become more popular recently than their counterparts.)
With some cases, it's obvious that removing the ing suffix would be bad (sometimes in a way I can't quantify) and thus there is no form without it (or it is exceedingly rare). Examples:
In any case, here is the data from Google NGrams for some pairs of words (click on an image to go to the Ngram page that generated it). You will see that the trends are all over the place:
As others have already pointed out, both swim and swimming are nouns (or a gerund) and can thus function as noun adjunct. With regards to the swim team specifically first the proof that the question has some merit. The ngrams are conclusive for overall English, American English and even British English the term is on a quick rise. The last being the only one where swimming team retains a lead.
If we consider other teams, the ten most popular (ngram) all feature actual nouns rather than gerunds. Of course the four sports don't have an -ing ending. We don't go footballing, baseballing or basketballing and tracking is something else entirely.
In fact in the top one hundred noun teams there are only the engineering, marketing and the training team with an -ing ending. Although all of them have dictionary entries in their own right, rather than being conceived as a gerund. The search in the British corpus is similar. Thus, one could argue, that at least for the swim team it's just aligning itself to all the other teams out there.
The truth seems to be that in modern English anything can function in the modifier position, so swimming club, swim club, are both fine. There's a slightly different feel, and of course a different rhythm, so probably in different circumstances one might prefer one form over the other.
Generally, when the root word can exist as either noun or verb, it would seem that either the noun or the gerund can behave as an attributive noun. Thus, either "hunt club" or "hunting club"; "swim suit" or "swimming suit"; and "shave foam" or "shaving foam". Common usage in various linguistic communities may tend to favor one form over another.
I haven't done any research to back this up, but perhaps we are seeing these changes for the following reasons:
Swimming club seems to denote a club that's swimming. Hence, swim club.
Shaving foam seems to denote a foam that's shaving. Hence, shaving foam.
Painting brush seems to denote a brush that's painting. Hence, paint brush.
Washing room seems to denote a room that's washing. Hence, wash room.
Given that we need our phrases to say what we intend them to say, this seems a logical development. The terms without -ing also have the virtue of having fewer characters. Plus, there is nothing grammatically incorrect about the non*-ing* forms.