because so many teams win championships by drafting players. No one besides the Spurs has done it in recent years.
#1 Draft Picks since 1990:
1990-Derrick Coleman (New Jersey)
1991-Larry Johnson (Charlotte Hornets)
1992-Shaquille O'Neal (Orlando)
1993-Chris Webber (Orlando-Golden State)
1994-Glenn Robinson (Milwaukee)
1995-Joe Smith (Golden State)
1996-Allen Iverson (Philadelphia)
1997-Tim Duncan (San Antonio)
1998-Michael Olowokandi (LA Clippers)
1999-Elton Brand (Chicago)
2000-Kenyon Martin (New Jersey)
2001-Kwame Brown (Washington)
2002-Yao Ming (Houston)
2003-LeBron James (Cleveland)
2004-Dwight Howard (Orlando)
2005-Andrew Bogut (Milwaukee)
2006-Andrea Bargnani (Toronto)
2007-Greg Oden (Portland)
2008-Derrick Rose (Chicago)
2009-Blake Griffin (LA Clippers)
2010-John Wall (Washington)
2011-Kyrie Irving (Cleveland)
2012-Anthony Davis (New Orleans Hornets)
2013-Anthony Bennett (Cleveland)
Only Duncan won a Championship with the team that drafted him. O'Neal and James won Championships, but with other teams. O'Neal, Iverson and Howard made it to the Finals with their draft team, but lost.
If you want to go back further, here are #1 picks who won Championships with the team that drafted them since the 1963 draft:
1966 - Cazzie Russell (Knicks)
1969 - Lew Alcindor (Bucks)
1974 - Bill Walton (Blazers)
1979 - Magic Johnson (Lakers)
1982 - James Worthy (Lakers)
1984 - Hakeem Olajuwon (Rockets)
1987 - David Robinson (Spurs)
That's 8 times total, and of those 8 times, twice the #1 pick joined a previous #1 pick - Duncan+Robinson, and Worthy+Johnson. Robinson was on the downward slope of his career, though, and he'd never won on his own, even with some great teammates, so how much did he mean to that win? The pick used to select Worthy was acquired in a trade, as the Lakers were already the reigning Champions, so again, this pick comes with an asterisk. It's also questionable if Cazzie Russell's 11 PPG were the reason the 69-70 Knicks won it all, or whether it was more to do with Willis Reed, Walt Frazier, and Dave DeBusschere.
So in 50 years, just 5 #1 picks have changed the direction of a franchise and taken them to a Championship - Alcindor, Walton, Johnson, Olajuwon, and Duncan, and only two of them won multiple titles with their drafting teams, so between them they have 10 rings with their drafting teams (and Johnson alone has five of those). This is what all you pro-tankers are getting bent out of shape over? A 25% chance of a 10% chance of maybe winning a Championship, when history says that the odds of winning are higher if you acquire players by other means (including a high draft pick that *isn't* #1)?