Well it's going up.
And until the announcement we don't know what AMC has in store for us.
But I would assume that if it's fantastic news (the way it looks atm) they would expect the share price to rise.
Why not wait until the price has spiked and then sell some more shares?
It would make it easier for AMC (VMC) to recover it's cost.

Only AMC knows I guess.
Maybe they just want to sell cheap shares to make everyone happy