Purdue signed 4, 4* HS kids between '18-'21
Avg class: 46
Iowa State had 3, HS 4* kids between '18-21
Avg class: 42
Miami had 8, 4* HS kids between '18-'21
Avg class: 36
Providence had 3, 4* HS kids between '18-21
Avg class: 77
Colorado had 4, 4* HS kids between '18-21
Avg class: 70
Only major transfer class I could find was Iowa State's '21 class which was 7 guys, which means most of those '18-'21 HS kids weren't even there anymore. Point is, those arent spectacular recruiting rankings. It's not some monumental task to make a sweet sixteen.
I think you just proved my point? All except Providence had twice as good recruiting rankings as the buffs. Talent wins basketball games. Only two teams had worse recruiting rankings between 18-21 than the buffs that made the sweet 16. So 2 out of 352 (division 1 teams) did something last year so that makes it easy?
Also, not all 4 stars are created equal: Tyrese Hunter was the 37th ranked player in the nation willed Iowa State to the sweet 16. He would have been the highest ranked commit in 247 database for the buffs (pre Cody).
Miami was led by Kameron McGusty 41st ranked player in 2016 would have been buffs highest rated commit in 247 database history, Isaiah Wong-79th ranked player in 2019- would have been buffs 5th highest ranked player recruited in 247 database history, Charlie moore 71st rated player in 2016 class- would have been 3rd highest buffs player recruited in 247 database histor, and Jordan Miller
Purdue was lead by Jaden Ivey- 89th ranked player in 2020 class would have been the buffs 6th highest rated player in 247 database history (KJ was 88th in 21)
Also Providence has been very transfer heavy and senior heavy. Providence starting 5 last year was Noah Horchler- transfer from North Florida, Al Durham- highly regarded Indiana transfer, Nate Watson 100th ranked player in 2017, Jared Bynum- highly regarded transfer from St. Joes, and AJ Reeves the 48th ranked player in 2018. 6th man was Justin Minaya highly regarded transfer from South Carolina. They also won 11 games by 5 points or less. Unheard of.
So every team except St. Peters in the sweet 16 last year had a player that would have been the highest or one of the rated recruits the buffs have had in the modern era, they recruit more consistently year in and year out so build better depth, and recruit some of the highest touted players from the transfer portal each year.