They are rather strict with these measures to prevent bonus abuse from players claiming it more than once. They generally don't allow more than one person per household to claim a welcome bonus or more than one person from the same IP address. The bonus terms and conditions vary from casino to casino, but there are specific terms that you'll find at most.
There is huge competition in the gambling industry, and operators have to set themselves apart from others with generous welcome bonuses, which are only available to new players and you can get them only once.
