Удивительно, но я только сегодня дочитал статью доконца. Она прекрасна во всём, не добавить, не убавить..
Why would they, is a good question. Just as why Polkadot would maintain the Parity client is a good question. They even have a bitcoin and BCH client. If you can get them to run it, why not have influence over as many chains as you can?