Playoff aspirations
Losing ground in a playoff race takes time, and a four-game lead lasts longer than you would expect. Even if a team has a 0-3 week, the team behind them would have to simultaneously go 3-0, and even then there is still a one-game separation.
Throw in a few 1-2 and 2-1 weeks? Those gaps can ebb and flow for quite some time before any noticeable changes happen. Memphis came out of the break with that four-game lead over 9th place Portland. Despite a 2-5 stretch, they still hold a three-game lead over now 9th place Sacramento.
Assuming the Grizzlies can string together a few short winning streaks and hopefully avoid any more five-game losing streaks, it would take a Herculean effort by one of the teams below them to catch up over the final 21 games.