BB is not tearing down, more like he is clearing the debris from the last tear down that was never even remotely re-built.
As to your comparisons, these programs are hardly cycling up fast - at Purdue, Brohm is in year 5 and his best regular season record is 6-6 (years 1 and 2) - in fact, prior to the Iowa upset, his seat was beginning to get warm. At Rutgers, Schiano is in year 2 - and he is 6-10 (3-10 in conference - of course, that's in the brutal Big Ten East). Matt Campbell has done better at ISU - albeit in the Big 12 - with winning records since year 2. But he did go 3-9 in year 1 and it did take him until year 5 to get his team ranked.
We are all impatient, but no one could turn this hot mess into a winner overnight.
When you pick the right coach, things can turn around relatively quickly.
Rutgers was 3-21 the three years preceding Schiano (.125). Schiano, in year 2, is 6-10 (.375) and 3-4 this year. By any measure, that's a swift change in direction, for the better. Very tough division, but recruiting is on the rise too.
Purdue was 8-27 the three years prior to Brohm (.229). Brohm is at (.460) in year 5, has been to two bowl games and is currently in the top 25. Notably, it was just a few years ago when this board was discussing Lovie and Brohm being of similar starting point, and debating which would be more successful. This is where Illinois should be, by now, dating back to Whitman's hire in Feb '16. We're not, we're still probably 5 years away from this.
Iowa State was also 8-27 in the three years preceding Campbell (.229). Campbell was 19-19 after three years and is 39-30 thru current (.565). Every one of Campbell's teams have been ranked during the season at some point, except his first team. And he's been to 4 bowl games in 5 full season, including a NY 6 bowl.
No one is looking for an overnight turn around, that just doesn't happen. But it's brutal to see how others are making progress, when Illinois is not. The Lovie hire set this program back 5 years but there's no point in rehashing that. I do believe BB will be successful at Illinois, but it's going to be a long, slow build.