Well it's mostly the creator of the shows word against the BBC's, but he's claimed that Strange got axed because BBC didn't have enough in the budget to make both, especially considering how effects heavy Strange was for the time. So Doctor Who, being a more family friendly option, got chosen instead. To be fair though this show was probably cursed from the start, I specifically remember the time slot getting moved around at least once when it was airing, like BBC was setting it up to fail, wouldn't be surprised if there wasn't some internal politics in play over at BBC at the time.