You can Report the seller to eBay, but it was eBay that installed the option that blocks incoming questions.
And it is an option.
Sellers are allowed to control how they sell their items. And again their items. No matter how much you want it, the seller is not required to accept your bid or even your questions.
Reasons for blocking questions usually come down to the location of the customer. If the seller is determined not to sell outside the USA (and remember this is a country where many people are quite convinced that Hawai'i is a small town in Kenya), why should they waste time answering questions from people who they are not interested in selling to?
Other available Blocks, which may or may not also Block questions, are Strikes for Unpaid Items, no active Paypal account, and negative feedback (as in -3%, not just a few red donuts).
Sellers can also cancel bids at will. I did that once because the bidder's ID gave me the willies.
Sellers can also Block specific buyers.