Perhaps because they don't want to actually block you from doing this, but want to have the plausible deniability that they put measures in place?

(And 'they' here might mean the company as an abstract entity, or perhaps just the engineer put in charge of implementing this feature?)

Validates output at time of rendering, so you can't trick it with obfuscation techniques.

There's a browser plugin called DeMod or something that disables it but I don't know how well it works.