I just ran through the last 20 years in my head, and this is surprisingly accurate. Top picks have simply not translated to championships. However, I would gently push back and assert that the previous 20 years (1980-1999) have included several good examples, listed below. Note that this covers every championship in this era except for the 1983 76ers.
Michael Jordan (3rd, 1984) 6 les for Bulls
Scottie Pippen (5th, 1987) 6 les for Bulls
Hakeem Olajuwon (1st, 1984) 2 les for Rockets
Larry Bird (6th, 1978) 3 les for Celtics
Kevin McHale (3rd, 1980) 3 les for Celtics
Magic Johnson (1st, 1979) 5 les for Lakers
James Worthy (1st, 1982) 3 les for Lakers
Isiah Thomas (2nd, 1981) 2 les for Pistons
Tim Duncan (1st, 1997) 1 le in this referenced era, but 5 total les for Spurs
David Robinson (1st, 1987) 1 le in this referenced era, but 2 total les for Spurs
So, how much of the change is due to the inherent variability of small sample sizes, and how much due to trends such as the increased frequency of stars moving to big markets and/or super teams? When I started writing this post, I was leaning toward the former, but now after collecting the information I think it's the latter. The shift starting in 2000 is jarring.