Scammers impersonate many different companies.

Not sure why you feel let down, as it has nothing to do with Ebay.

Sending their numbers to Ebay spoof won't make any difference.

Ebay cannot track these numbers and not is  it under any obligation to do so.

I've had calls and SMS's from from scammers pretending to be from such places as Amazon, the ATO, Aus Post, Medicare and several different banks, but I definitely understand that has nothing to do with these organisations so I don't go around blaming them for something that is not their responsibility. 

It is, however,  100% the responsibility of the recipient of such calls to either ignore/don't answer and never give out any information if you do speak to someone. Personally I will never answer the phone unless it is someone in my contacts list. Genuine callers leave messages, scammers hang up without doing so and I always block those numbers.