I imagine because it takes more effort to do wired Internet than a home wireless phone. Fido uses Rogers for its internet an it's easy to do so because Fido is owned by Rogers. Plus the flanker brands traditionally stick to phone services. Fido seems to be the outlier here.
Remember Rogers does not have home phone wired infrastructure and uses Fido to supplement there (overpriced) network. Wireless or internet based services still have some issues over wire lines and both Bell and Telus have to support there systems in the markets they serve.