Just because SF hasn't been buying B&M's doesn't mean they won't in the future. There have been several changes in the controlling interest in the company which has been resulting in some (much needed) changes in direction. Look for increased budgets for maintenance and for CapEx in the coming years.
SeaWorld SD and SFMM really don't draw from the same market (except for park fans/enthusiasts). Even with Mako, SFMM could add a bigger, better B&M dive coaster and market it. SeaWorld is really concentrating on their local market and so is SFMM. They are not "destination parks" for 99% of the public.