I wondered the same thing. You would think that betting on the match should not be under the jurisdiction of the tennis club, rather the gambling regulators.
I fail to see how someone electronically (or otherwise) relaying non-confidential information about a tennis match would in any way harm the integrity of the match.
Of course, courtsiders are simply transmitting factual information: they aren't harming the integrity of the games at all.
The integrity of those involved in catching, apprehending, and banning courtsiders for life, on the other hand, is certainly in question.