Scheduling and travel.
That's true for this year. But we would've loved LA squared in the Finals last year. Spurs/Lakers could've made some nice Finals in the past. It's not like every Finals is a compelling matchup. It's a crapshoot. You actually have a greater chance of having that compelling Finals if you aren't limited by conferences.
If schedules and travel limit you a conference then it should stay that way for the postseason. Now if the league is gonna change things to play East/West teams 41x a year each then it makes sense but if your conference and division still makes up 60% and 20% of your schedule you should be battling other conference teams 4 times of 7 till the best of each meet.

