That argument reduces down to “because a market exists” — is that really a compelling justification for this particular additional tax?

Because the dollars being used to pay for the digital good have already been taxed, probably many times over, by the time the credit card transaction settles and the merchant account is credited at the end of the week (or whenever).

It’s reasonable to question if this particular tax was designed in a way to target specific foreign companies, without a compelling nexus, which would make the tax predatory.