Well I think that's changed recently.
But yeah, generally 1st picks got 3 mill for 4 years...with the last one being an option year (that was generally picked up as the player was a young guy on a cheap contract)
The point was very much to address the unintended consequences of the NFL system. That the 1st rounders would gradually command bigger contracts. This means bad teams invest a huge amount of cap on 50/50 players. If it doesn't work out you are in big trouble.
In the NBA, you might shatter a franchise for a decade if they were to sign #1's to NFL style contracts and he was a bust.