If the founders retain a majority, this is less than 4% of their stake — that percentage is more relevant in analyzing the confidence signalling and motivations than a superficially large "$21 million" figure.
Clearly you still don't understand. They didn't sell 4% of their stake. If they did that, it would be somewhat reasonable. What they got was a dividend. In other words a bonus.
And yes the figure is still "large" because it is 1/6th of their funding that goes to their pockets, rather than the company.
