Because the trendy media choice this season is “not falling for Miami again”.
The truth is, it would take incredibly bad luck and/or serious injuries for Miami not to improve on last season’s record. We’re talking about a team that lost 5 games by 7 or less. Compared to just two wins by 7 or less. Statistically, these thing tend to even out over time. (Just like all the narrow wins in 2017 became losses in 2018)
So, even if the team doesn’t improve (hard to believe it won’t) they’d still be in line for 1-2 more wins this season based off averages alone.