BDA is a high end, seasonal destination that is not conducive to mass transportation.
US-Canada transborder has high taxes which makes either hub operations which favor smaller aircraft (which is why there is such a larger number of RJs) or to/from Florida, CA, or other high volume destinations - but WestJet and others are heavily in those markets already. For WN to decide they want to get into those markets, means they are going to have to push hard to gain a decent share of the market.... I doubt WN will do consider it worth it.
there are far more opportunities to Latin America and the Caribbean.