Yes VISA 100% without a doubt could make more money by processing transactions incorrectly in some cases.

Foe example they could cause transactions that go to some startup company they consider a threat to their business model to fail some of the time, causing damage to the entity by making them seem flakey/unreliable, or costing them money in having to provide other payment options, or ask customers for payment again. Or they could fuck with payments to big businesses in certain countries in an attempt to manipulate exchange rates in a way as to maximize profits as reported is USD, etc.

Alternatively it is very possible that in some cases VISA may decide to act in ways that don't maximize profits. This may sound surprising, but it is extremely common. First of all, companies operating on incomplete information will sometimes make decisions they think will maximize profits, but that actually wont. Or you get plenty of CEOs that decide to pull off dumb stunts to try to boost this quarter's numbers to better match analysts predictions, at the cost of reduced future profit. Companies are often sufficiently opaque that such things are not always immediately obvious.

This is especially problematic for something like VISA, which gets to arbitrarily set the network rules. It is not like your business can just say, ok then VISA, I'll send transactions for your cards over the MasterCard network instead.

Having a system that gets processed by a large number of different mutually distrustful entities helps avoid all this. It is unlikely that all or even most of them will view your startup as a threat. There will most likely be at least some that really are trying to maximize profits. And among those with slightly different goals (which are usually still somewhat of an approximation of maximizing profits), it is unlikely that a large majority, will deviate from expected behavior in exactly the same way (if they do, it would effectively be some of that 50+% collusion, even if it was accidentally rather than deliberate). The rules for the network cannot be arbitrarily changed on the whims of a single central entity.

For somebody running a business, who does not particularly trust that some American run Card network wont fuck with their transactions, a crypto based payment network could legitimately look far nicer. They can more reliably predict the behavior of the network with respect to a transaction they send/receive. The network does not have a lot of arbitrary rules, and those rules don't change very often. Foreign governments you don't trust are less likely to be able to meddle in your transactions, etc.

And to be clear, I'm no crypto shill. Realistically it gets used for wild speculation, scams, illegal or frowned upon transactions. There are some (but big picture still not all that many) legitimate entity to entity transactions not tied to somebody using crypto as speculative investments. I see that "Smart contracts" (which are neither smart nor contracts) while interesting are still deeply flawed, and realistically have limited uses not better performed by centralized systems. Etc. And all of that is not even considering the environmental caused by the use of work.