If a team is very close to the salary cap, they may not have enough money to draft a player until one of their players are drafted off of their team. If you are within $377k of your player payroll budget, you can't draft a player because you need at least $327k for the player's salary plus the $50k draft fee.
For example, if your team has $315k left in your player payroll budget when it is your turn in the first round, you won't be able to draft. If a player from your team is drafted by another franchise after your turn and the removal of that player's salary puts you to at least $377k of remaining player payroll, you could take a player in a future round.