Castilian Spanish uses a lisp with that letter combination; hence the "th".
What makes it even more confusing is that, just like with English, you can pronounce a name any way you like if it is your name. I've known at least several (maybe many; I lose track) folks from the "new world" who pronounced their Spanish or Portuguese or Italian origin names the way the immigrants pronounced it...even if that immigration occurred centuries ago. My last name is Celtic, and when I run into someone from the British Isles they invariably pronounce it the way the old world says it...utterly different from how I say it. Same sort of thing.
Agree that it is sheer laziness, bordering on incompetency, for an announcer to not bother to check name pronunciation. Keith Jackson used to consider it to be one of the hardest aspects of his job...which he approached as a professional, and checked in advance with a team rep for any new team he was announcing. He took notes. Of course, the team rep occasionally didn't know what he/she was talking about, and Keith also occasionally goofed up...at which point he would actually apologize on the air if it was pointed out to him during an intermission. I always respected that.
