Their range is strong, but you have position and 500bb of implied odds — the math favors patient calls.
4-betting narrows to the very top; suited hands with nut potential call more. The question on every street becomes: which hands are happy getting 500bb in?
The big blind 3-bets your cutoff steal. The discount made their call cheap — the 3-bet means they chose not to take it.
Assumes a standard 3-bet; 4-bet to ~2.2–2.5x the 3-bet. Deep, favor calls over 4-bets — a 4-bet pot at 500bb+ commits you with range disadvantage.