I believe most people who follow their twitter and registering on the sites are not real gamblers. Most of them are just trying to get the giveaway. It is just too good to be true for a new site to spend more than 6btc for free on pre launch celebration. It is OK to register to get the giveaway to know how the site works once it is launched officially. Still, depositing once it is alive is not recommended at all.
yeah,many people use Twitter to see giveaways and that new gambling sites know that ,that's why they use that platform to advertise the new gambling sites.
If they are serious for promotion they can make announcement thread here and make more giveaway 2k sats is not too generous its normal giveaway same as your website having a faucet and free to claim for new user's.