Some hockey teams are stronger than others in terms of fanbases. The Detroit Red Wings and Boston Bruins are two obvious teams. The Chicago Blackhawks would've been too, but they had a complete idiot for an owner who refused to televise games, feeling it would impact the number of ticket sales. Only a few years ago did he die and his kid inherit the team and promptly get a tv contract. And sports tend to be held on a higher rank over UPN, syndication, even down to the NHL. WB had pre-emptions, though Tribune was able to bully some stations into dropping their sports teams once the contracts ended.
Also, back during Voyager's run, more hockey, basketball, baseball games were broadcast over-the-air instead of on regional sports networks (RSNs; cable channels) which meant more pre-emptions. You have to look at UPN as a whole, which had pathetic ratings. Voyager was their best show/2nd best, SmackDown was their best show too. Their sitcoms were low, Voyager's companion shows (Nowhere Man, The Sentinel, 7 Days) were comparable to weak syndicated shows, and its shows didn't have a desirable niche like young white adults/teens or generate chatter like WB's shows. WB had more star power than UPN. Look at how many stars went somewhere, even briefly vs. UPN.
I've got a partial list of the teams that interrupted episodes of Voyager and what episodes, though the data's raw and hasn't quite been refined yet and has some big gaps. Something I'd like to eventually test is to see if Voyager was pre-empted as much as syndicated shows were.