Its not hard. Its capital intensive with a low profit margin. So it doesn't attract a lot of competition because you can make more money in other ways that have moats. There are at least a dozen other chat apps, some of which are decades old.

To have a successful chat business, you need the network effect of lots of users (big marketing spend), you need lots of capital for operations (big spend on disks and compute) and after all that you get only a few dollars per user. Its just not a great business on the balance sheet. Notice that quality software doesn't even get a mention in this niche.