It is a huge percentage of their funding, around 1/6th. If a company where to raise 6m and the founders got 1m not by equity, but by dividends! That just doesn't happen.
If the founder's want to sell some of their equity, I'm fine with that, but that is NOT what happened here. This is purely a pay-day.
If I knew my company was going to be the next eBay for realestate, why would you hamper your company by taking 21m off the table. This signals greed and/or being unsure of your future success.