HTTPS is not free. Game developers are usually very performance-sensitive. If you're not transmitting any sensitive data, it may seem appealing to forgo the seemingly-needless HTTPS overhead.
Also, most games I have played seem to use HTTPS. The only time it is used is when the game does not need an instant result, in which case they use HTTP or HTTPs. Most of the times, this is in the main menu or similar. Doing this makes it even harder (assuming they use certificate pinning) for users to change the values returns to gain any advantage on their client.
Any part of the game that needs speed should be using a UDP based protocol.
If your game is executing js (as for the example given by the GP), you are transmitting sensitive data. In that scenario not only confidentiality but even more integrity of the data is important.