The went with a streaming service because they all have a none compete clause in their contracts from the BBC that ran through I believe its March of 2017 ,they had all but sign with ITV , ITV was even going to air the new show at the same time as Top Gear, but the lawyers got involved, the clause is only for the UK, so with Amazon(Netflix was also in the bidding for them) all based in the US, that gets them around that clause.
All I can really say is, I cant wait for them to be back next year.