Mobile providers had no incentive to let the instant messaging services on their network when they were charging 10 cents per SMS message.
IMHO, the reason a mobile first network was more compelling than a desktop first network is that people tend to have their phones on them, while their desktops tend to be at their desks. For better or worse, you can always reach me on my phone.
Tencent developed QQ on desktop and then WeChat on mobile, but afaik, didn't bridge the two networks.