TL:DR WeChat was too big for phones back few years ago when many people didn't have space to spare and data was expensive and slow. WhatsApp compressed files so they loaded quicker and you could keep more of them.
Then in 2016, Tencent for some reason invested in Hike Messenger when it was already in trouble. Hike was created by the son of a telecom guy. Sorta if the son of Verizon's CEO created an instant messenger app and got investment and support from his dad and the company.