Over the last three years, starting with 2017, there have been 16, 10, and 13 first-round freshmen drafted, including ten of the first eleven in 2017. Nine of the last 11 first overall picks have been freshmen.
College basketball is a team sport, but the best players remain the best players. Basketball is unique because each player has an outsize impact - McIntosch, at 36 mpg, accounts for 18 percent of "player-minutes". A great slugger is still only one-ninth of at-bats, a great hockey goal-scorer is still only on the ice ~40% of the time, a great QB only plays half the time and is worthless without five fat guys doing their jobs.
The best college teams turn over half their rotation every year. Kentucky turns over everybody.