How much profit would ASML lose to this ban? Maybe they'll get a couple hundred million dollars in annual compensation from the U.S. gov?

The bigger worry is China pushing a home grown company to produce the same equipment and provide whatever state resources they need.

Hard to protect against espionage and hard to compete with a company that has massive state subsidies.

Easier to just sell them the equipment to prevent this.

Note: they can already produce DUV equipment, just probably not economically viable (yet)