I think I'm either misreading your comment, or there's a misunderstanding here.
When RSUs are issued, they typically appreciate in value due to either an increase in share price or a discount or both.
When the RSUs vest, one of 2 things happens: either the number of shares is reduced by a sum equivalent to pay income taxes, or (more rarely) income taxes are paid by the recipient later at tax time. In either case, the shares didn't exist in the recipient's account before that vesting date.
If the shares are sold, those funds can be used to buy other shares if desired. If they are held, they are just normal shares in that company. In either case, they appreciate as capital gains instead of income, starting with the point in time when they were either purchased or vested whichever the case may be.