The GPL allows commercial use, provided that you ship the source code to the software bundled with the GPL3 source code you use to your customers. Publish a mobile app on any app store with a GPL3 snippet and suddenly you must provide the source code to your entire app under GPL3 terms. That in turn might violate the licenses for the other libraries you use, so mixing libraries might permanently leave you open to lawsuits from either copyright owner.

The GPL also inherently violates the Apple App store guidelines, so you cannot use any GPL snippets for iOS applications you plan to publish there.

There's workarounds for GPL requirements (notable the web loophole, writing applications that don't distribute binaries but generate web content instead, thereby not violating the GPL by not providing the backend source code) but even that has dangers (for example, when you include a snippet of GPL3 code in your (compiled) Javascript code).

> what would the GPL violation be in this case?

Since it incorporates GPL source code, the entire copilot neural network needs to distributed under the GPL and - since it is a non-source form of the software - it's entire corresponding source (namely, the entire training dataset it was generated from) needs to be made available, also under the GPL, to anyone it's distributed to. (AGPL is a bit^Wlot more clear about the fact that remote interaction over a network is a kind of distribution, though.)

GPL allows commercial use. Under certain conditions.