It's not really about the size of the fanbase in Florida specifically, or the short-term ratings. There's a limit to how many committed fans will jump on board with the Panthers, and there's no question that the Bruins draw more eyes to TV screens that Florida ever could. The league knows this. What it's about for the NHL is national coverage and the size and scale of the footprint they have in North America as a whole. Having competitive, prominent teams in more places and more states is attractive for both advertisers and broadcasters. You can reach more markets, and diffusion across a greater area is ultimately beneficial, with more scope for long-term growth, even if the immediate viewership in raw numbers is smaller. It makes the league look bigger and more important and enhances its reputation.
So the incentive to favor the Panthers, representing a pretty big state, is there. And the league also know that most New England hockey fans will keep watching no matter what, and in that sense they can largely take them for granted.
I always like to approach things from the point of view of don't blame conspiracy or bias for what can otherwise be ascribed to sheer incompetence or stupidity. But the last couple of days have made that difficult. Very hard to put the two decisions you mentioned merely down to different interpretations. Thinking the league has an agenda here actually makes the most sense as an explanation.