Arsenal having money in the bank doesn’t mean Arsene is aloud to spend it, simples really.
Kroenke is financing huge investments by securing huge loans. To secure these loans he borrows against his assets, ie his Arsenal shares as a loan security. To get larger loans with lower interest he needs to insure Arsenal has a high liquidity, ie cash in the bank. To maximise loan value he also needs to ensure Arsenal is turning a profit, high spending would show a loss on our accounts and would mean a lender wouldn’t offer as favourable rates.
Arsenal’s cash is probably banked in the same bank Kroenke’s borrowing from. By doing that Kroenke could offset Arsenal savings against any loan, despite Kroenke only owning 67% of AFC he could do a deal to offset any loans against 100% of AFC’s cash reserves.