Nobody is going to pay you before you do the work, but “Time value of money means it’s better to be paid money today than in 5 years”
Thus, 10M in RSU that vest in 5 years > 10M in cash today (not a real option) > 10M in cash in 5 years.
However, this also helps explain 5%,15%, 40%, 40% vesting schedules they are somewhat better than 25%,25%,25%,25% for the company because it better incentivizes staying and for the employee due to tax advantages.