Apparently the amortization due on some of those players is huge e.g. Pjanic signed last year on a 4 year deal for 60m so it would be 45m.
And their wages are so high that no one wants them, they'd have to pay them off - I believe Griezmann is on 600K a week.
Amortization just means the cost of the purchase is spread over the length of the contract. If they sell him, or he leaves on a free transfer it goes away.
It's why they did the deal with juve in the first place. They "sold" arthur to juve for €65m. Juve "sold" pjanic to barca for €50m. That meant that for accounting purposes barca got €65m and juve got €45m. When in reality only €15m swapped hands. Because it is amortised over say a 5 year contract barca only "spent" €10m on pjanic the season they got him. Leaving them €55m up for that season. Problem is for the next 4 years they still have to "pay" €10m a season in amortisation.
It' a quick fix to balance the books.